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Proc. Nat. Acad. Sci. U S A Vol. 7 0 , N o . 11, p p . 3195-3199, November 1973 Plasma Membranes from Cultured Muscle Cells: Isolation Procedure a n d Separation o f Putative Plasma-Membrane Marker Enzymes (Na+, K+-ATPase/5'-nucleotidase/a-bungarotoxin) STEVEN D . SCHIMMEL, CLAUDIA KENT, RICHARD BISCHOFF, AND P . ROY VAGELOS Departments o f Biological Chemistry a nd Anatomy, Washington University School o f Medicine, S t . Louis, Missouri 63110 Contributed b y P . R oy Vagelos, M a y 2 9 , 1973 ABSTRACT Partially purified plasma membranes were obtained from chick-embryo muscle cells grown i n tissue culture. Th e purification procedure involved homogeniza- tion i n buffered isotonic sucrose followed b y differential a n d sucrose density gradient centrifugations. Th e activi- ties o f five plasma-membrane markers, a s well a s micro- somal a n d mitochondrial markers, were followed through- o ut the purification. When cultures were labeled with [1251]a-bungarotoxin, which binds t o thesurface o f cultured muscle cells, t h e distributions o f bound a-bungarotoxin a n d Na+,K+-ATPase ( E C 3.6.1.3) activity were nearly identical. Th e activities o f these t wo plasma-membrane markers were maximal i n th e upper two fractions o f t h e sucrose density gradient a n d were purified 5 - t o 7-fold with respect to total particulate protein. These fractions contained 20-30% o f t h e Na+,K+-ATPase activity a n d bound a-bungarotoxin, 4%/c o f t h e microsomal marker TPNH- dependent cytochrome c reductase, 0.2% o f t h e mito- chondrial marker succinate-dependent cytochrome c reductase, 2.7%c of t h e cellular RNA, a n d 0.02%vo o f t h e DNA. Th e activity o f t h e commonly used plasma-membrane marker, 5'-nucleotidase ( E C 3.1.3.5), wa s l ow i n t h e upper t wo sucrose gradient fractions a n d wa s maximal i n a more dense fraction. Th e distributions ofthe other t w o plasma-membrane markers, leucyl J - naplithylamidase a n d phosphodiesterase I , were intermediate between Na+,K+-ATPase a n d 5'-nucleotidase. Th e distributions o f al l markers were similar i n preparations from cultures containing mononucleated myogenic cells, multinucleated myotubes, fibroblasts, o r al l three cell types. Modifica- tion o f t h e procedure t o include homogenization i n t h e absence o f sucroseresulted i n a 3.4-fold purification o f t h e membranes containing 5'-nucleotidase, which were shifted t o a lower density. Mononucleated muscle cells grown in tissue culture fuse t o form multinucleated myotubes which elaborate muscle- specific proteins a n d eventually contract spontaneously (1). Under appropriate conditions i n vitro more than 8 0 % o f t h e cells i n culture m a y fuse t o form myotubes (2). (For a recent review, s e e ref. 3 . ) However, t h e mechanism by which fusion occurs i s unknown, although i t i s reasonable t o expect that alterations i n t h e cell surface must play a vital role. I n order t o elucidate such fusion-related surface alterations, w e have undertaken a study o f th e plasma membranes o f chick-embryo muscle cells grown i n monolayer culture. I n this paper w e report t h e isolation of plasma membranes from cultured muscle cells a t various stages in their development and th e separation o f t w o widely accepted plasma-membrane "marker" enzymes, 5'-nucleotidase ( E C 3.1.3.5) and ouabain- sensitive Na+- plus K+-stimulated adenosine triphosphatase (Na+,K+-ATPase, E C 3.6.1.3). (For a review o f plasma- membrane isolation and characterization techniques, s e e ref. 4 . ) To examine further t h e significance o f t h e separate distributions o f these lplasma-membrane markers, we labeled muscle cultures with radioactive a-bungarotoxin, which blocks acetylcholine receptors ofskeletal muscle ( 5 ) a n d binds t o t h e surface o f mnyotubes i culture ( 6 , I n subcellular fractions o f cells labeled with [1251]a-bungarotoxin, t h e tribution o f bound toxin w a s nearly identical t o t h e distribu- tion o f Na+,K+-ATPase b u t n ot o f 5'-nucleotidase. MATERIALS AND METHODS Culture Conditions. Fertilized chicken eggs were obtained from Ken-Roy Hatcheries, Bergen, M o . Cultures o f muscle cells from 12-day chick embryos were prepared essentially a s described ( 8 ) except that cells were preplated f o r 1 0 m i n a t 3 7 0 t o remove some o f t h e fibroblastic cells which adhere quickly t o t h e (9). T h e cells were diluted t o 0.35-0.5 X 1 0 6 cells p e r m l i n culture medium [82.4% Eagle's minimum essential medium, 8.3% horse serum (Grand Island Biological Co., Grand Island, N.Y.), 8.3% chick-embryo extract (high- speed supernate o f quickly frozen 5 0 % extract o f 11-day embryos i n Earle's balanced salt solution) a n d 1 % antibiotic- antimycotic solution (GIBICO) ] , a n d 20 m l were added t o each 150-mm collagen-coated dish. T h e cultures were incubated a t 3 7 0 i n a humidified atmosphere a t 5 % CO2-95% air, a n d 1 0 m l o f culture medium w a s replaced daily. To obtain cultures o f nonfused myogenic cells, w e used 5 f i g o f 5-bromodeoxyuridine (BrdU; Nutritional Biochemicals Co., Cleveland, Ohio) p e r m l o f culture medium (10, 11). For cultures o f myotubes, 5-fluorodeoxyuridine (FdU; Calbio- chem, L a Jolla, Calif.), a t a final concentration o f 1 0 ,AIM, w a s added t o cultures 36-48 hr after they were plated (12). After a n additional 24-48 h r , nearly a ll dividing mononucleated cells h a d detached from the dish a n d nondividing myoblasts h a d fused into myotubes. Fibroblasts were obtained from subcutaneous connective tissue i n the groin region o f 12-day chick embryos, plated a t 0.25 X 1 0 f cells p e r m l a n d grown f o r 3 days. T h e cells were then subcultured a t t h e same density a n d harvested after 2 days. Isolation o f Plasma Mllembranes. Monolayer cultures o f muscle cells o r fibroblasts were washed four times with cold Earle's salt solution; thei 1 0 m l o f Earle's salt solution w a s 3195 Abbreviations: BrdU, 5-bromodeoxyuridine; FdU, 5-fluoro- deoxyuridine; TE A triethanolamine.

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P r o c . N a t . A c a d .S c i .USAVo l .7 0 ,N o . 1 1 ,p p .3 1 9 5 - 3 1 9 9 ,N o v e m b e r1 9 7 3

P l a s m aMembrane s f r o mC u l t u r e dM u s c l eC e l l s :I s o l a t i o n P r o c e d u r ea n dS e p a r a t i o no f P u t a t i v ePlasma-Membrane Marke r Enzymes

( N a + ,K + - AT P a s e / 5 ' - n u c l e o t i d a s e / a - b u n g a r o t o x i n )

STEVEND . SCHIMMEL ,CLAUDIAKENT, RICHARD BISCHOFF, AND P . ROY VAGELOS

D e p a r t m e n t so fB i o l o g i c a lC h e m i s t r ya n dA n a t o m y ,Wa s h i n g t o nU n i v e r s i t yS c h o o lo fMed i c i n e ,S t .L o u i s ,M i s s o u r i6 3 1 1 0

C o n t r i b u t e db yP . R o yVa g e l o s ,May 2 9 ,1 9 7 3

ABSTRACT P a r t i a l l y p u r i f i e d p l a sma memb r a n e s we r eo b t a i n e df rom ch i ck - embryo musc l e c e l l sg r own i n t i s s u ec u l t u r e . Th e p u r i f i c a t i o np r o c e d u r ei n v o l v e dhomogen i za -t i o n i n b u f f e r e d i s o t o n i c s u c r o s e f o l l o w e d by d i f f e r e n t i a la n d s u c r o s e d e n s i t y g r a d i e n t c e n t r i f u g a t i o n s .Th e a c t i v i -t i e s o f f i v ep l a sm a -m emb r a n e m a r k e r s , a s we l l a s micro-soma l a n d m i t o c h o n d r i a lm a r k e r s ,were f o l l o w e dt h r o u g h -

ou t t h e p u r i f i c a t i o n . Whe n c u l t u r e s were l a b e l e d with[ 1 2 5 1 ] a - b u n g a r o t o x i n ,wh i c h b inds t o t h e s u r f a c eo f c u l t u r e dmus c l e c e l l s ,t h e d i s t r i b u t i o n s o f b o u n d a - b u n g a r o t o x i na n d Na+,K+-ATPase ( E C 3 . 6 . 1 . 3 )a c t i v i t y wer e n e a r l yi d e n t i c a l . Th e a c t i v i t i e s o f t h e s e two p l a s m a -m em b r a n emarke r s were max ima l i n t h e u pp er t wo f r a c t i o n s o f t hes u c r o s e d e n s i t y g r a d i e n t a n d wer e p u r i f i e d 5 - t o 7 - f o l dw i t h r e s p e c t t o t o t a l p a r t i c u l a t e p r o t e i n . These f r a c t i o n sc o n t a i n e d20 -30% o f t h e N a + , K + - AT P a s ea c t i v i t y a n d b o u n da - b u n g a r o t o x i n ,4 % / co f t h e mic ro soma l ma r k e r TPNH-

dependen t c y t o c h r ome c r e d u c t a s e , 0 .2% o f t he mi to -c h o n d r i a l ma r k e r s u c c i n a t e - d e p e n d e n tc y t o c h r ome cr e d u c t a s e ,2 . 7 % co f t h e c e l l u l a r RNA, a n d 0 . 0 2% v oo f t h e DNA.Th e a c t i v i t y o f t h e c ommo n l y used p l a s m a -m em b r a n em a r k e r , 5 ' - n u c l e o t i d a s e( E C 3 . 1 . 3 . 5 ) ,wa s l ow i n th e u p p e rtwo s u c r o s e g r a d i e n tf r a c t i o n s a n d was max im a l i n amo r e dense f r a c t i o n . Th e d i s t r i b u t i o n s o f t h e o t h e r t wo

p l a sm a -m emb r a n e m a r k e r s , l e u c y l J - n a p l i t h y l a m i d a s ea n d p h o s p h o d i e s t e r a s e I , we r e i n t e r m e d i a t e be tweenNa+,K+-ATPase a n d 5 ' - n u c l e o t i d a s e .Th e d i s t r i b u t i o n s o fa l l marke r s were s i m i l a r i n p r e p a r a t i o n sf r om c u l t u r e sc o n t a i n i n gmononu c l e a t e d myog e n i c c e l l s ,m u l t i n u c l e a t e dmyo tube s , f i b r o b l a s t s , o r a l l t h r e e c e l l t y p e s . M o d i f i c a -t i o n o f t h e p r o c e d u r et o i n c l u d e h o m o g e n i z a t i o ni n t h eabsence o f s u c r o s e r e su l t e di n a 3 . 4 - f o l d p u r i f i c a t i o no f t h emem b r a n e s c o n t a i n i n g 5 ' - n u c l e o t i d a s e , which weres h i f t e d t o a l o w e r d e n s i t y .

M o n o n u c l e a t e dmu s c l e c e l l sg r o w ni n t i s s u ec u l t u r e f u s et of o r m m u l t i n u c l e a t e dm y o t u b e sw h i c h e l a b o r a t emu s c l e -s p e c i f i cp r o t e i n sa n d e v e n t u a l l yc o n t r a c t s p o n t a n e o u s l y( 1 ) .U n d e ra p p r o p r i a t ec o n d i t i o n si n v i t r om o r et h a n 80% o f t h ec e l l si n c u l t u r emay f u s et o f o r mm y o t u b e s( 2 ) .( F o r a r e c e n t

r e v i e w ,s e er e f .3 . )H o w e v e r ,t h e m e c h a n i s mb y w h i c hf u s i o no c c u r s i s u n k n o w n ,a l t h o u g hi t i s r e a s o n a b l et o e x p e c t t h a ta l t e r a t i o n si n t h ec e l ls u r f a c e m u s t p l a ya v i t a lr o l e .I n o r d e rt o e l u c i d a t es u c h f u s i o n - r e l a t e ds u r f a c ea l t e r a t i o n s ,w e h a v eu n d e r t a k e na s t u d yo f t h e p l a smam e m b r a n e so f c h i c k - e m b r y omu s c l e c e l l sg r o w ni n m o n o l a y e rc u l t u r e .I n t h i sp a p e r w er e p o r t t h e i s o la t i o n o fp l a s m a m e m b r a n e sf r o m c u l t u r e dmu s c l e c e l l sa t v a r i o u s s t a g e si n t h e i rd e v el o p me n t a n dt h es e p a r a t i o no f t w o w i d e l y a c c e p t e dp l a s m a - m em b r a n e

" m a r k e r "e n z ym e s ,5 ' - n u c l e o t i d a s e( E C3 . 1 . 3 . 5 )a n d o u a b a i n -s e n s i t i v eN a + -p l u sK+ - s t i m u l a t e da d e n o s i n et r i p h o s p h a t a s( N a + , K + - AT P a s e ,E C 3 . 6 . 1 . 3 ) .( F o r a r e v i e w o f p l a s m a -m e m b r a n ei s o l a t i o na n d c h a r a c t e r i z a t i o nt e c h n i q u e s ,s e er e f .4 . ) To e x a m i n ef u r t h e rt h e s i g n i f i c a n c eo f t h e s e p a r a t ed i s t r i b u t i o n so f t h e s e l p l a s m a - m em b r a n ema r k e r s ,we l a b e l e dmu s c l e c u l t u r e sw i t h r a d i o a c t i v ea - b u n g a r o t o x i n ,w h i c hb l o c k sa c e t y l c h o l i n er e c e p t o r so f s k e l e t a lmu s c l e ( 5 )a n d b i n d st o t h e s u r f a c e o fmn y o t u b e si n c u l t u r e( 6 , 7 ) . I n s u b c e l l u l a rf r a c t i o n so f c e l l sl a b e l e dw i t h [ 1 2 5 1 ] a - b u n g a r o t o x i n ,t h e d i s -t r i b u t i o no fb o u n dt o x i nw a s n e a r l y i d e n t i c a lt o t h e d i s t r i b u -t i o no fN a + , K + - AT P a s eb u t n o t o f5 ' - n u c l e o t i d a s e .

MATER IALSAND METHODS

C u l t u r eC o nd i t i o n s . F e r t i l i z e dc h i c k e n e g g s w e r e o b t a i n e df r o m K e n - R o yH a t c h e r i e s ,B e r g e n ,M o . C u l t u r e s o f mu s c l ec e l l sf r o m 1 2 - d a yc h i c k e m b r y o sw e r e p r e p a r e de s s e n t i a l l ya s d e s c r i b e d ( 8 )e x c e p tt h a t c e l l sw e r e p r e p l a t e df o r 1 0 m i na t 3 7 0 t o r em ov e s om e o f t h e f i b r o b l a s t i cc e l l sw h i c ha d h e r eq u i c k l y t o t h e d i s h( 9 ) .T h e c e l l sw e r ed i l u t e dt o 0 . 3 5 - 0 . 5X1 0 6c e l l sp e r m l i n c u l t u r emedium [ 8 2 . 4 %E a g l e ' smin imume s s e n t i a lm ed i u m, 8 . 3 %h o r s e s e r u m ( G r a n dI s l a n d B i o l o g i c a lC o . ,G r a n dI s l a n d ,N . Y. ) ,8 . 3 %c h i c k - e m b r y oe x t r a c t ( h i g h -s p e e d s u p e r n a t e o f q u i c k l yf r o z e n 50% e x t r a c t o f 1 1 - d a ye m b r y o si nE a r l e ' sb a l a n c e ds a l ts o l u t i o n )a n d 1% a n t i b i o t i c -a n t i m y c o t i cs o l u t i o n( G I B I C O )] ,a n d2 0m l w e r ea d d e dt o e a c h1 5 0 - m mc o l l a g e n - c o a t e dd i s h .T h ec u l t u r e sw e r e i n c u b a t e da t3 7 0i n a h u m i d i f i e da t m o s p h e r ea t 5% C O 2 - 9 5 %a i r , a n d 1 0m l o fc u l t u r em e d i u mw a sr e p l a c e dd a i l y .To o b t a i n c u l t u r e so fn o n f u s e dm y o g e n i cc e l l s ,w e u s e d 5 f i g

o f 5 - b r om o d e o x y u r i d i n e( B r d U ; N u t r i t i o n a lB i o c h e m i c a l sC o . ,C l e v e l a n d , O h i o )p e rm l o f c u l t u r emedium ( 1 0 ,1 1 ) .F o r c u l t u r e so fmy o t u b e s ,5 - f l u o r o d e o x y u r i d i n e( F d U ;Ca l b i o -c h em ,L a J o l l a ,C a l i f . ) ,a t a f i n a lc o n c e n t r a t i o no f1 0 , A I M ,w a sa d d e dt o c u l t u r e s3 6 - 4 8 h ra f t e rt h e y w er ep l a t e d ( 1 2 ) .A f t e ra n a d d i t i o n a l2 4 - 4 8 h r , n e a r l ya l l d i v i d i n gm o n o n u c l e a t e dc e l l sh a d d e t a c he d f r o mt h e d i s ha n d n o n d i v i d i n gm y o b l a s t sh a d f u s e di n t omy o t u b e s .F i b r o b l a s t s w e r e o b t a i n e d f r o ms u b c u t a n e o u sc o n n e c t i v et i s s u ei n t h e g r o i nr e g i o no f 1 2 - d a yc h i c k em b r y o s ,p l a t e da t 0 . 2 5 X 1 0 fc e l l sp e rm l a n d g r o w nf o r3 d a y s .T h ec e l l sw e r et h e n s u b c u l t u r e da t t h e s a m ed e n s i t ya n dh a r v e s t e da f t e r2 d a y s .

I s o l a t i o no f P l a s m aM l l em b r a n e s .M o n o l a y e rc u l t u r e so fmu s c l e c e l l so r f i b r o b l a s t sw e r ew a s h e df o u r t i me s w i thc o l dE a r l e ' ss a l ts o l u t i o n ;t h e i 1 0 m l o fE a r l e ' ss a l ts o l u t i o nw a s

3 1 9 5

A b b r e v i a t i o n s : B r d U , 5 - b r o m o d e o x y u r i d i n e ;F d U , 5 - f l u o r o -d e o x y u r i d i n e ;TE A t r i e t h a n o l am i n e .

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3 1 9 6 B i o c h em i s t r y : S c h i mm e le ta l .

TABLE 1 . D i s t r i b u t i o na n d a c t i v i t i e so f p r o t e i na n d s u b c e l l u l a rm a r k e r si n t h ef r a c t i o n a t i o no f S - d a ymu s c l ec u l t u r e s

[ 1 2 6 5 ]< - L e u c y l TPNH- S u c c i n a t e -B u n g a r o - N a + ,K + - 5 ' - N u c l e o - P h o s p h o - p - n a p h t h y l - c y t o c h r o me c y t o c h r oc

F r a c t i o n P r o t e i n t o x i n * AT P a s e t i d a s e d i e s t e r a s eI a m i d a s e c r e d u c t a s e r e d u c t a s e

H o m o g e n a t e ,p a r t i c u l a t e( 1 0 0 ) 1 3 . 1 (1 00 ) 1 7 . 8 ( 1 00 ) 5 . 1 1 ( 1 0 0 ) 6 . 0 8 ( 1 00 ) 3 . 0 9 ( 1 0 0 ) 9 . 0 0 ( 1 0 0 ) 1 4 . 3 ( 18 . 9 9 t 1 1 8 , 0 0 0 $ 1 6 1 § 4 6 . 0 § 5 4 . 6 § 2 7 . 8 § 8 0 . 8 § 1 2 9 §

1 7 0 0X g S u p e r n a t e ( 3 2 . 8 )2 8 . 1 ( 7 0 . 5 ) 3 0 . 2 ( 5 5 . 5 ) 7 . 2 6 ( 4 6 . 3 ) 9 . 5 9 ( 5 1 . 9 ) 4 . 8 8 ( 5 1 . 8 )1 3 . 5 ( 4 9 . 5 ) 9 . 4 3 ( 2 1 . 5 )

1 7 0 0X g P e l l e t ( 8 0 . 6 ) 5 . 1 (3 1 . 3 ) 1 0. 6( 47 . 7 )2 . 54 (6 2 . 8) 4 . 0 7 (5 3 . 3 )1 . 7 4 ( 4 5 . 3 ) 5 . 7 4 ( 5 2 . 0 ) 1 7 . 3 ( 9 7 . 6 )2 8 , 0 0 0X g S u p e r n a t e ( 6 . 0 ) 1 1 . 0 ( 5 . 1 ) 9 . 0 ( 3 . 1 ) 1 . 8 0 ( 2 . 1 ) 3 . 1 3 ( 3 . 1 ) 2 . 1 0 ( 4 . 1 ) 2 . 8 0 ( 1 . 9 ) 0 . 7 6 ( 0 . 3 )2 8 , 0 0 0X g P e l l e t ( 2 1 . 5 ) 3 3 . 0 ( 5 4 . 6 ) 3 8 . 8 ( 4 6 . 6 ) 8 . 7 3 ( 3 6 . 8 ) 1 1 . 3 ( 4 0 . 0 )5 . 2 4 ( 3 6 . 3 ) 1 5 . 4 ( 3 6 . 8 ) 6 . 8 8 ( 1 0 . 3 )I + I I ( 4 . 3 ) 9 3 . 6 ( 2 9 . 8 )9 4 . 1 ( 2 2 . 8 ) 4 . 3 5 ( 4 . 3 ) 1 7 . 9 ( 1 2 . 7 )8 . 0 8 ( 1 2 . 9 )8 . 9 9 ( 4 . 4 ) 0 . 5 8 ( 0 . 2 )To t a l g r a d i e n t ( 2 0 . 3 ) ( 5 2 . 0 ) ( 4 5 . 3 ) ( 3 2 . 4 ) ( 3 6 . 8 ) ( 4 2 . 1 ) ( 2 7 . 8 ) ( 1 9 . 2

3 - D a ymu s c l ec u l t u r e sw e r ep r e p a r e da n d f r a c t i o n a t e da sd e s c r i b e di nMe t h o d s .Enzyme a c t i v i t i e sa r ee x p r e s s e da s n m o lm i n - 'm g op r o t e i n- l .N um b e r si np a r e n t h e s e sa r et h e p e r c en t r e c o ve r yo ft h e i n i t i a la c t i v i t yi nt h ep a r t i c u l a t eh o m o g e n a t e .

* c p m / A u go fp r o t e i n .t mg o ft o t a lp r o t e i ni nt h ep a r t i c u l a t eh o m o g e n a t e .t To t a lc p m .§ To t a la c t i v i t i e s ,e x p r e s s e da sn m o lp e r m i n .

a d d e dt o e a c h 1 5 0 - m md i s h .T h ec e l l sw e r er e m o v e df r o mt h e

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s m a l l s h e e to fp e r f o r a t e d c e l l o p h a n e( M i c r o b i o l o g i c a lA s s o c i a t e s ,B e t h e s d a ,M d . ) a n d c o l l e c t e db y c e n t r i f u g a t i o nf o r 5 m i n a t 1 1 0 0 X g . ( A l lc e n t r i f u g a lf o r c e sr e f e rt o r a v . . )T h i s a n d a l ls u b s e q u e n ts t e p sw e r e d o n ea t 0 C 4 ' .T h e c e l lp e l l e tw a s s u s p e n d e di n 1 5 m l o f 0 . 2 5Ms u c r o s e - 1 mM t r i e t h a n o l a m i n e( T E A )*H C l ( p H 7 . 4 )( s u -c r o s e - T E A )p e r g o fc e l l s( w e tw e i g h t ) .T h ec e l l sw e r eb r o k e ni na D o u n c eh o m o g en i z e r ( K o n t esG l a s sC o . ,Vi n e l a n d ,N . J . )w i t h t h et i gh t ( B )p e s t l e .F i f t e e nu p - a n d - d o w ns t r o k e sw e r es u f f i c i e nt f o rc omp l e t eb r e a k a g e ,a s j u d g e db y p h a s ec o n t r a s tm i c r o s c o p y .T h e h o m o g e n a t ew a s c e n t r i f u g e df o r 1 0 m i n a t1 7 0 0 X g ; t h es u p e r n a t ew a s r e m o v e da n d c e n t r i f u g e df o r60 m i na t e i t h e r2 7 , 0 0 0o r3 3 , 0 0 0X g .A s l i g h t l yb e t t e ry i e l do f p l a sm am em b r a n e sw a s o b t a i n e dw i t h 3 3 , 0 0 0X g , a n d

t h a tc e n t r i f u g a lf o r c ei s n ow u s e d r o u t i n e l y .The r e s u l t i n g4l N a + , K + - AT P a s e[ l 2 5 1 ] a - P h o s p h o - L e u c y l

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F I G .1 . R e l a t i v e d i s t r i b u t i o no f m a r k e r a c t i v i t i e so n t h es u c r o s e d i s c o n t i n u o u sd e n s i t y g r a d i e n t .3 - D a ymu s c l e c u l t u r e sw e r e l a b e l ed w i t h [ 1 2 5 I ] a - b u n g a r o t o x i n ,h om o g e n i z e di n s u c r o s e -TEA, a n df r a c t i o n a t e d .F r a c t i o n sw e r ec o l l e c t e da t e a c hi n t e r f a c ea s f o l l o w s :I ( 8 . 3 - 2 0 %s u c r o s e ) ;I I ( 2 0 - 2 7 % ) ;I I I ( 2 7 - 3 2 % ) ;IV ( 3 2 - 4 0 % ) ;a n d V ( 4 0 - 5 5 % ) .T h i s i s t h e s ame e x p e r i m e n ta ss h o w ni nTa b l e 1 .R e l a t i v es p e c i f i ca c t i v i t yw a sc a l c u l a t e da s t h ep e r c e n ti n e a c hf r a c t i o no f t h et o t a la c t i v i t yr e c o v e r e df r o m t h eg r a d i e n td i v i d e db y t h e p e r c e n t i n t h a tf r a c t i o no f t h e t o t a lp r o t e i nr e c o v e r e df r o mt h e g r a d i e n t .

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p o s i t i o n : 0 . 5m l o f 5 5% ( w / w )s u c r o s e ,t h e n 2 . 5m l e a c h o4 0 % ,3 2 % , 2 7% ,a n d20% s u c r o s e .A f t e r c e n t r i f u g a t i o ni n a n SW 4 1 r o t o r a t4 1 , 0 0 0 rpm

( 2 0 6 , 0 0 0X g ) f o r1 . 5h r ,t h eb a n d so f t u r b i dm a t e r i a la t t h ei n t e r f a c e si n t h e g r a d i e n tw e r e r e m o v e da n d d e s i g n a t e daf o l l o w s :8 . 3 - 2 0 % ,I ; 2 0 - 2 7 % ,I I ; 2 7 - 3 2 % ,I I I ; 3 2 - 4 0 %I V ; a n d 4 0 - 5 5 % ,V . E a c h f r a c t i o nw a s d i l u t e dt o a b o u t 9m l w i t h 1 mM TEA*HCl ( p H 7 . 4 ) ,t h e n c o l l e c t e db y c e nt r i f u g a t i o nf o r60 m i n a t 1 0 5 , 0 0 0X g .T h e p e l l e t sw e r e s u sp e n d e di n TEA. HC l a n d a s s a y e d f o rp r o t e i na n d e n z y ma c t i v i t i e s .S am p l e sw e r ea l s ot a k e na t e a c hs t e po fp r e p a r ab e f o r e t h eg r a d i e n ts t e p ,d i l u t e dw i t h TEA*HC l , a n d c e nt r i f u g e df o r6 0 m i n a t 1 0 5 , 0 0 0X g , s o t h a to n l y p a r t i c u l

p r o t e i n . w a sa s s a y e df o re n z y m ea c t i v i t y .A t l e a s t3 0 m i n be -f o r e d i lu t i o na n d c e n t r i f u g a t i o n ,b e e f - p a n c r e a sd e o x y r i b on u c l e a s eI ( S i g m aC h e m i c a lC o . ,S t .L o u i s ,Mo . ) , a t a f i n ac o n c e n t r a t i o no f 5 0 u g / m l ,w a s a d d e d t o t h e s amp l e s o fh om o g e n a t e a n d1 7 0 0 X g p e l l e tt o f a c i l i t a t el a t e rr e s up e n s i o nf o r a s s a y .A l lc o n d i t i o n sw e r e k e p t t h e s a m e f o rp r e p a r a t i o n sh o m o g e n i z e di n TE A H C l i n s t e a do f T E A - s uc r o s e ,e x c e p t t h a ta 1 5 , 0 0 0X g c e n t r i f u g a t i o ns t e pw a ss u b s tt u t e df o rt h e3 3 , 0 0 0X g c e n t r i f u g a t i o ns t e p .

[ ' 2 5 I f a - B u n g a r o t o x i n .P u r e a - b u n g a r o t o x i nw a s a g i f tf r o mD r . R e g i sB . K e l l y .I t w a s l a b e l e d w i t h 1 2 5 Ib y t h e p r o c e d u r eo fB e r ge t a l . ( 5 ) ,w i t h 0 . 5mg o f t o x i na n d 5 mCi o f c a r r i ef r e eN a ' 2 1 I( I n d u s t r i a lN u c l e a rC o . ,S t .L o u i s ,Mo . ) .To l a b e

c u l t u r e sw i t h r a d i o a c t i v et o x i n ,t h ec e l l si n a 1 5 0 - m md i s hw e r ew a s h e dt w i c ew i t h E a r l e ' ss a l ts o l u t i o n ,t h e n i n c u b a t e df o r1 0 m i na t 3 7 0i n 1 0 m l o f c u l t u r em e d i u mc o n t a i n i n g3 0p m o l ( 8 . 5X 1 0 ' fc p m ) o f [ 1 2 I ] c a - b u n g a r o t o x i n .T h e t o x i nc o n t a i n i n gm e d i u mw a s r e m o v e da n d t h ec e l l so n t h e d i s hw e r e w a s h e df o u rt i m e s i n E a r l e ' ss a l ts o l u t i o nc o n t a i n i2 m g / m lo f b o v i n e - s e r u ma lbu mi n , t h ent w i c e w i t h E a r l e 's a l ts o l u t i o nb e f o r et h e y w e r eh a r v e s t e d .A d d i t i o no f 1 mMc a r b a m y l c h o l i n et o t h ei n c u b a t i o nm i x t u r er e s u l t e di n a 9 0 - -9 5 %d e c r e a s ei n b i n d i n go f l a b e l e d .t o x i n .1 5 I - C o n t a is a m p l e sw e r ec o u n t e do n a P a c k a r dm o d e l3 0 0 1A u t o - G a m mS p e c t r o m e t e r .

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P r o c .N a t . A c a d .S c i .USA 7 0 ( 1 9 7 3 )

B i o c h em i c a l D e t e r mi n a t i o n s .5 ' - N u c l e o t i d a s ew a s a s s a y e di n a 0 . 1 - m li n c u b a t i o nm i x t u r ec o n t a i n i n g5 0 mM g l y c i n e -HCl ( p H 8 ; 7 ) ,0 . 2mM EDTA, 0 . 2l u go f s o d i u md o d e c y ls u l f a t ep e r o a go fp r o t e i n ,6 mM a d e n o s i n e - 5 ' - m o n o p h o s p h a t e ,a n d 5 - 2 0Mgo fp r o t e i n .T h er e a c t i o nw a s c a r r i e do u t f o r3 0 -6 0 m i n a t 3 7 0a n d t e r m i n a t e db y a d d i t i o no f0 . 1m l o f 10%p e r c h l o r i ca c i d .T h e p r e c i p i t a t e dp r o t e i nw a s r e m o v e db yc e n t r i f u g a t i o na n d t h e i n o r g a n i cp h o s p h a t ec o n t e n t o f t h es u p e r n a t ew a s d e t e r m i n e d( 1 3 ) .O u a b a i n - s e n s i t i v eN a + , K + , -AT P a s ew a sd e t e r m i n e di n a 5 0 - A lr e a c t i o nm i x t u r ec o n t a i n -i n g3 0 mM i m i d a z o l e - HC l( p H 7 . 5 ) ,0 . 1 1M N a C 1 ,1 5 mMKC l , 5 mM N a N 3 ,0 . 5mM e t h y l e n e g l y c o l - b i s ( j 3 - a m i n o e t h y le t h e r ) N N ' - t e t r a a c e t i ca c i d( E G TA ) ,4 mM MgC l 2 ,3 mMAT P , a n d 2 - 3 0 , u go fp r o t e i n .N a + , K + - AT P a s ea c t i v i t yw a sc a l c u l a t e da st h ed i f f e r e n c ei nAT P a s ea c t i v i t yi n t h e p r e s e n c ea n d a b s e n c eo f1 mM o u a b a i n .R e a c t i o n sw e r ec a r r i e do u t a t3 7 0 f o r4 5 m i n a n d s t o p p e db y a d d i t i o no f 5 0Muo f 1 0 %p e r -c h l o r i ca c i d .A f t e rr e m o v a lo f p r o t e i nb y c e n t r i f u g a t i o nt h ei n o r g a n i cp h o s p h a t ec o n t e n tw a sd e t e r m i n e d( 1 3 ) .I n mu s c l e -c e l lh om o g e n a t e s ,3 5 - 5 0 %o f t h e t o t a lAT P a s ea s s a y e d i nt h e p r e s e n c e o f Na+ a n d K+ w a s o u a b a i ns e n s i t i v e .F o rp u r i f i e dp l a s m a - m e m b r a n ef r a c t i o n s( I a n d I I ) f r o mmu s c l e

c e l l s ,t h ei n h i b i t i o nw a s6 0 - 8 5 % .T h e s p e c t r o p h o t om e t r i ca s s a y sf o rT P N H - d e p e n d e n ta n ds u c c i n a t e - d e p e n d e n tc y t o c h r o m ec r e d u c t a s e sw e r ee s s e n t i a l l yt h o s ed e s c r i b e db y S o t t o c a s ae t a l . ( 1 4 ) .P h o s p h o d i e s t e r a s eIw a s d e t e r m i n e da s d e s c r i b e db y To u s t e r e t a l .( 1 5 ) ,e x c e p tt h a tt h er e a c t i o nw a st e r m i n a t e db y a d d i t i o no f 0 . 4M NaOHa n d t h ea b s o r b a n c ea t 4 0 0nm w a sme a s u r e dd i r e c t l y .L e u c y l, B - n a p h t h y l a m i d a s e( l e u c i n ea m i n o p e p t i d a s e )w a s a s s a y e da sd e s c r i b e db y Hu b s c h e re ta l .( 1 6 ) .P r o t e i nw a sd e t e r m i n e db yt h e m e t h o do f L o w r ye t a l . ( 1 7 )w i t h b o v i n e - s e r u ma l b um i n( P e n t e x ;Mi l e sL a b o r a t o r i e s ,I n c . ,K a n k a k e e ,I l l . )a ss t a n d a r d .T h ed i s t r i b u t i o no fDNA o rRNA i n s u b c e l l u l a rf r a c t i o n sw a sd e t e rm i n e di n p r e p a r a t i o n sf r o m c u l t u r e sg r o w nf o r3 d a y si n t h e p r e s e n c eo f 3 MM[ m e t h y l - 3 H ] t h y m i d i n e( 0 . 5, u C i / m l ;New E n g l a n dN u c l e a rC o r p . ,B o s t o n ,Ma s s . ) o r 3 MM[ 5 -3H j u r i d i n e( 0 . 5MC i / m l ;S c h w a r z / M a n n ,O r a n g e b u r g ,N . Y. ) .

EXPERIMENTAL RESULTS

P u r i f i c a t i o n o fF r a c t i o n sE n r i c h e di n N a + , K + - AT P a s e .3 -D a y - o l dmu s c l ec u l t u r e sw e r e l a b e l e dw i t h [ 1 2 5 I ] a - b u n g a r o -t o x i n ,h a r v e s t e d ,h o m o g e n i z e di n s u c r o s e - T E Ab u f f e r ,a n df r a c t i o n a t e db y d i f f e r e n t i a la n d s u c r o s ed i s c o n t i n u o u sd e n s i t yg r a d i e n tc e n t r i f u g a t i o n s .T h e r e s u l t s o fa t y p i c a lp u r i f i c a t i o np r o c e d u r ea r es h o w ni nTa b l e 1 .R e c o v e r i e so fp r o t e i n , r a d i o -a c t i v i t y ,a n d a l lme a s u r e de n z y m a t i ca c t i v i t i e sw e r e c l o s et o 1 0 0 %i n e a c h s t e p o ft h e p u r i f i c a t i o n .I n t h e 1 7 0 0 X gc e n t r i f u g a t i o ns t e p ,e s s e n t i a l l ya l lo f t h e n u c l e i( 9 8 . 8 %o f t h et o t a lDNA) a n d a b o u t 80% o f t h e m i t o c h o n d r i a lm a r k e r ,

s u c c i n a t e - d e p e n d e n tc y t o c h r o m ec r e d u c t a s e ,w e r e f o u n d i nt h e p e l l e t .I n a d d i t i o n ,6 3 %o ft h e 5 ' - n u c l e o t i d a s ea n d48% o ft h e N a + , K + - AT P a s ew e r e f o u n d i n t h e p e l l e tf r a c t i o n ,a p -p a r e n t l ya s s o c i a t e dw i t h t h el a r g ep a r t i c l e s .M o r ev i g o r o u sh om o g e n i z a t i o nw i t h a mo t o r - d r i ve np e s t l e .d i d n o t a l t e rt h er e s u l t .A f t e rt h e 2 8 , 0 0 0X g c e n t r i f u g a t i o n ,a l lb u t 6% o f t h er e m a i n i n gp a r t i c u l a t ep r o t e i nw a sf o u n di nt h e p e l l e t .T h e d i s t r i b u t i o no f t h e 2 8 , 0 0 0X g p e l l e tm a t e r i a lo n a

d i s c o n t i n u o u ss u c r o s eg r a d i e n t i s s h o w ni n F i g .1 . I n t h eg r a d i e n ts h o w ni n F i g .1 , [ 1 2 5 1 ] a - b u n g a r o t o x i nr a d i o a c t i v i t ya n d N a + , K + - AT P a s ew e r e d i s t r i b u t e ds i m i l a r l yw i t h ma x i -mum s p e c i f i ca c t i v i t i e si n f r a c t i o n sI a n d I I .5 ' - N u c l e o t i d a s e ,

o n t h e o t h e rh a n d , w a sl o w i n t h o s ef r a c t i o n sa n d m a x i ma li n f r a c t i o nI V . T h ed i s t r i b u t i o n so fl e u c y l, B - n a p h t h y l a m ia n d p h o s p h o d i e s t e r a s eI , w h i c hh a v e a l s ob e e n r e p o r t e d t ob e p l a s m a - m em b r a n em a r k e re n z y m e s( 4 ,1 5 ) ,w e r e n e a r l yi d e n t i c a la n d w e r e i n t e r m e d i a t eb e t w e e nt h o s eo f N a + , K + -AT P a s ea n d5 ' - n u c l e o t i d a s e .T h e o v e r a l l p u r i f i c a t i o no f N a + , K + - AT P a s ei n f r a c t i o n s

I a n d I I c o m b i n e dw a s 5 . 3 - f o l d( w i t hr e s p e c tt o p a r t i c u l a t e

p r o t e i n ) ,w i t h a 23% y i e l do f e n z y m ea c t i v i t y .I n t h i ss a m ep r e p a r a t i o n ,s p e c i f i cr a d i o a c t i v i t yo f [ 1 2 5 I] I a - b u n g a r o t oi n c r e a s e d7 . 2 - f o l dw i t h a 3 0% y i e l do f r a d i o a c t i v i t y .T h ep u r i f i e dm e m b r a n ef r a c t i o n s( I a n d I I )c o n t a i n e d4 . 4 %o ft h ei n i t i a lT P N H - d e p e n d e n tc y t o c h r o m ec r e d u c t a s e ,a n e n z y m ec o m m o n l yu s e d a s a m i c r o s o m a lm a r k e r ( 1 8 ) ,0 . 2 %o f t h en i i t o c h o n d r i a lm a r k e r s u c c i n a t e - d e p e n d e n tc y t o c h r o m ecr e d u c t a s e ,0 . 0 2 %o f t h e t o t a lc e l l u l a rDNA, a n d 2 . 7 %( 1 8 3Mg /m go f p r o t e i n )o f t h e c e l l u l a rRNA. T h e m i c r o s o m a lma r k e r , T P N H - d e p e n d e n tc y t o c h r o m ec r e d u c t a s e ,w a sm a x i m a li n f r a c t i o nI V bu t d i f f e r e df r o m5 ' - n u c l e o t i d a s ei ni t sd i s t r i b u t i o ni n f r a c t i o n sI V a n dV . U n d e ro t h e r c o n d i t i o n s( s e eb e l o w )t h e s et w oma r k e r sd i f f e r e de v e n more d i s t i n c t l y .T h em i t o c h o n d r i a lm a r k e r ,s u c c i n a t e - d e p e n d e n tc y t o c h r o m e

c r e d u c t a s e ,w a s f o u n di n f r a c t i o n sI V a n dV .

P u r i f i c a t i on o fa F r a c t i o nE n r i c h e di n 5 ' - N u c l e o t i d a s e .F o rf u r t h e rs t u d y o f t h e m e m b r a n e sc o n t a i n i n gt h e s e p a r a t e dm a r k e r a c t i v i t i e s ,N a + , K + - AT P a s ea n d 5 ' - n u c l e o t i d a s e ,i tw a sn e c e s s a r yt o o b t a i n f r a c t i o n st h a t w e r e e n r i c h e df o ro n em a r k e rb u t t h at c o n t a in e do n l y l o w l e v e l so f t h e o t h e r .T h i sc o n d i t i o nw a s s a t i s f i e df o rN a + , K + - AT P a s ei n f r a c t i o n sIa n d I I o ft h e m e m b r a n ep r e p a r a t i o nd e s c r i b e da b o v e . I nt h i ss a m ep r e p a r a t i o n ,h o w e v e r ,t h e r ew a s n oo v e r a l lp u r i f i c a -t i o na n do n l ya 4% y i e l do f5 ' - n u c l e o t i d a s ea c t i v i t yi nf r a c t i o nI V ,w h e r et h i sa c t i v i t yw a sm a x i m a l .When c e l l sw e r eh om o g e n i z e di n s u c r o s e - T EA ,a b o u t6 3 %

o f t h e5 ' - n u c l e o t i d a s ea c t i v i t yw a s f o u n d i n t h e p e l l e ta f t e r

c e n t r i f u g a t i o na t 1 7 0 0X g f o r1 0 m i n . I f ,h o w e v e r ,a p o r t i o no f t h e s a m e c e l l sw a s s u s p e n d e da n d h om o g e n i z e di n 1 mMTE A H C 1 ( p H 7 . 4 ) ,w i t h o u t s u c r o s e ,o n l y2 0 - 4 0 %o f t h e5 ' - n u c l e o t i d a s ew a sr e c o v e r e di n t he 1 7 00X g p e l l e t ,a n d t h ed i s t r i b u t i o no f t h e r e m a i n i n g5 ' - n u c l e o t i d a s ewa s m a x i m a li n f r a c t i onI I Ir a t h e rt h a n f r a c t i o nI V ( F i g .2 ) .F r a c t i o nI I Ii n t h e TE A p r e p a r a t i o nc o n t a i n e d3 6 . 2 %o f t h e t o t a l5 ' -n u c l e o t i d a s er e c o v e r e df r o mt h eg r a d i e n t ,c o r r e s p o n d i n gt o ay i e l do f1 5 . 5 %o ft h et o t a lh o m o g e n a t ea c t i v i t ya n da p u r i f i c a -t i o no f3 . 4 - f o l d .

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F I G .2 . Re l a t i v e d i s t r i b u t i o no fm a r k e ra c t i v i t i e sf r o m3 - d a ymu s c l e c u l t u r e s a f te rh om o g e n i z a t i o ni n 1 mM T E A .H C 1( p H 7 . 4 ) .S u c r o s ed e n s i t y g r ad i e n tc o n d i t i o n swere t h e s am e a sd e s c r i b e df o rF i g .1 . To t a l p r o t e i na n d a c t i v i t i e sr e c o v e r e df r o mt h e g r a d i e n tw e r ea s f o l l o w s :p r o t e i n ,2 . 0 2mg ;N a + , K+ - AT P a s e ,6 8 . 3nmo l /m i n ;5 ' - n u c l e o t i d a s e ,1 9 . 7nmo l /m i n ;T P NH - d e p e n -d e n t - c y t o c h r o m ec r e d u c t a s e ,1 5 . 0nmo l /m i n .

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f r o mB r d U -a n d F d U - g r o w nc u l t u r e s ,3 - d a yc u l t u r e s ,a n d f i b r o -b l a ~ s t ~ s .T h i s i s t h es a m ee x p e r i m e n ta s s h o w ni nTa b l e 2 .S u c r o s ed e n s i t y g r a d i e n tc o n d i t i o n sw e r e t h e s a m e a s d e s c r i b e df o rF i g .1 .H a t c h e da r e a ,5 ' - n u c l e o t i d a s ea c t i v i t y .

I n c o n t r a s t t o t h e l a r g ec h a n g ei n5 ' - n u c l e o t i d a s ed i s t r i b u -t i o ni n t h e p r e l i m i n a r yf r a c t i o n sa n d on t h e s u c r o s e g r a d i e n t ,t h e r ewas l i t t l ec h a n g ei n t h e d i s t r i b u t i o n s o fa - b u n g a r o t o x i nr a d i o a c t i v i t y ,N a + K + - AT P a s e ,l e uc y l j B - n a p h t h y l a m i d a s e ,p h o s p h o d i e s t e r a s eI , o r T P N H - d e p e n d e n tc y t o c h r o m ecr e d u c t a s ei nc e l l sh o m o g e n i z e di nTEA. T h e s u c c i n a t e - d e p e n -d e n t c y t o c h r o m ec r e d u c t a s e ,h o w e v e r ,was s h i f t e di n r e l a t i v ed i s t r i b u t i o nb e t w e e nf r a c t i o n sIV a n dV on t h e g r a d i e n t .

M e m b r a n eP r e p a r a t i o n sf r o m M o n o n u c l e a t e dC e l l sa n dMy o t u b e s .3 - D a y - o l dc u l t u r e sc o n t a i nmy o t u b e s ,n o n f u s e dm y o g e n i cc e l l s ,a n d f i b r o b l a s t s .I n o r d e r t o d e t e r m i n ei f t h es e p a r a t i o no fN a + , K + - AT P a s ea n d 5 ' - n u c l e o t i d a s ea c t i v i t i e swas a r e s u l to f t h e h e t e r o g e n e o u sc e l lp o p u l a t i o n ,i t was

n e c e s s a r y t o d e t e r m i n et h e d i s t r i b u t i o no fm a r k e r sf r o mmore

h o m o g e n e o u sc u l t u r e s .A c c o r d i n g l y ,we p r e p a r e dm e m b r a n ef r a c t i o n sf r o mc u l t u r e so fe a c ho f t h e t h r e e c e l lt y p e s .Mono-n u c l e a t e dm y o g e n i cc e l l swe r e grown i n t h e p r e s e n c e o fBrdUt o r e v e r s i b l yi n h i b i tf o r m a t i o no fm y o t u b e s( 1 0 ,1 1 ) .F dU was

u s e d t o o b t a i n c u l t u r e sw i t h l a r g en u m b e r so fm y o t u b e sa n df e w m o n o n u c l e a t e dc e l l s( 1 2 ) .F i b r o b l a s t swe r e c u l t u r e d as

d e s c r i b e di n Me t h o d s .A l l t h r e e c e l lt y p e s we r e h o m o g e n i z e di n s u c r o se - T EA a n dw e r e f r a c t i o n a t e da s d e s c r i b e d a b o v e .I n e a c h c a s e , t h e d i s t r i b u t i o n so f a l l m a r k e ra c t i v i t i e sw e r e

s i m i l a rt o t h o s e s h o w ni n F i g .1 f o r3 - d a yc u l t u r e s .Th e d i s -t r i b u t i o n so f 5 ' - n u c l e o t i d a s ea n d N a + , K + - AT P a s ew e r e

n e a r l y i d e n t i c a lf o r t h e d i f f e r e n tc e l l t y p e s a n d f o r 3 - d a yc u l t u r e s( F i g .3 ) .E a c h s h o w e dt h e same c l e a rs e p a r a t i o no ft h e s et w oma r k e r s . I n a d d i t i o n ,t h e p u r i f i c a t i o na n d y i e l do fN a + , K + - AT P a s ei n g r a d i e n t f r a c t i o n sI p l u sI I was v e r y

s i m i l a rf o re a c hp r e p a r a t i o n( Ta b l e2 ) .When FdU- a n dBrdU-g r o w n c e l l sw e r e l a b e l e dw i t h [ 1 2 5 I I a - b u n g a r o t o x i nb e f o r eh a r v e s t ,t h e d i s t r i b u t i o no f r a d i o a c t i v i t yon t h e g r a d i e n tc l o s e l yf o l l ow e d t h a t o f N a + , K + - AT P a s e .( F o r B r d U - g r o w nc e l l s ,s p e c i f i cb i n d i n go f t h e t o x i n was l e s st h a n 7 % o f t h a tf o u n dw i t h3 - d a yc u l t u r e s ) .

DISCUSSION

I n t h i sp a p e r we r e p o r t t h e i s o l a t i o na n d p a r t i a l p u r i f i c a t i o no f p l a s m am e m b r a n e sf r o mmu s c l ec e l l sg r o w n i n t i s s u ec u l -t u r e . The p u r i f i c a t i o np r o c e d u r e i n v o l v e s d i f f e r e n t i a la n ds u c r o s e d i s c o n t i n u o u sd e n s i t y g r a d i e n t c e n t r i f u g a t i o n s .Oner e s u l to f t h i sw o r ki s t h e u n u s u a l l y c l e a rs e p a r a t i o no f t w oe n z ym e s c o m m o n l yu s e d a s m a r k e r sf o r p l a s m am e m b r a n e ,N a + , K + - AT P a s ea n d 5 ' - n u c l e o t i d a s e .T h i s s e p a r a t i o no c c u r si n membrane p r e p a r a t i o n sf r o m b o t h m us c lec e l l sa n d f i b r o -b l a s t s .To o u r k n ow l e d g e ,t h e s u b c e l l u l a rl o c a t i o no f t h e s e

e n z y m a t i cma r k e r si nc u l t u r e dmu s c l ec e l l sh a s n o t p r e v i ob e e n e s t a b l i s h e d .I n E h r l i c ha s c i t e st u m o r c e l l s ,5 ' - n u c lt i d a s ew a s d e t e c t e db y h i s t o c h e m i c a lt e c h n i q u e so n t h en u c l e a rm e m b r a n eb u t n o t o n t h e p l a s m am e m b r a n e( 1 9I t i s p o s s i b l et h a ti n c u l t u r e dmu s c l e c e l l s5 ' - n u c l e o tl i k e w i s emay b e a b s e n t f r o m t h e p l a s m am e m b r a n e .P e r d ua n d S n e i d e r( 2 0 )p u r i f i e dp l a s m a m e m b r a n e sf r o m c h i ce m b r y of i b r o b l a s t sa n d o b t a i n e ds i m i l a r p u r i f i c a t i oo f 5 '

n u c l e o t i d a s ea n d N a + , K + - AT P a s ea c t i v i t i e si n t h e i rmem-b r a n e f r a c t i o n .B e c a u s et h e d i s t r i b u t i o n sa n d r e c o v e r i eot h e s et w o e n z y m e sw e r e n o t r e p o r t e d ,h o w e v e r ,c o m p a r i sw i t h t h ep r e s e n t f i n d i n g si sd i f f i c u l t .T h er e h a ve b ee nr e p o ro f t h e s e p a r a t i o no f N a + , K + - AT P a s ea n d 5 ' - n u c l e o t ia c t i v i t i e s i nm e m b r a n ep r e p a r a t i o n s f r o m l i v e r ( 2 1 - 2E v a n s ( 2 2 )f o u n d t h a t t h e 5 ' - n u c l e o t i d a s ef r o mm o u s el i v ew a s p r e s e n t i n a f r a c t i o no f sma l l v e s i c l e swh i l e N a + , K +AT P a s ew a sp r e s e n t i na d en se rf r a c t i o no fl a r g em e m b r a n os h e e t s .T h e N a + , K + - ATP a s ew a s a s s o c i a t e dw i t h t h e l a r gj u n c t i o n a lc omp l e x e sw h i c ha r e c h a r a c t e r i s t i c o fl i v e rc e ls u r f a c e s .I nt h i sr e p o r tw eh a v ed e m o n s t r a t e dt h a t a - b u n g a r ot o x i n ,w h i c hb i n d st o n i c o t i n i ca c e t y l c h o l i n e r e c e p t oo n t h es u r f a c eo fc u l t u r e dmu s c l ec e l l s( 6 ,7 ) ,w a s p r e s e n t i n mem-

b r a n ef r a c t i o n st h a t a l s oc o n t a i nN a + , K + - AT P a s e ,i n d i c a tt h a tt h i sAT P a s ei s a c t u a l l yo n t h e s u r f a c eo fmu s c l e c e l l s( I nt h ee x p e r i m e n ts h o w ni n Ta b l e 1 , a l a r g e rp e r c e n t a g eo fa - b u n g a r o t o x i nt h a nN a + , K + - AT P a s er e m a i n e di n t h e s u p e r -n a t e a f t e rc e n t r i f u g a t i o na t 1 7 0 0X g ;h o w e v e r ,i n a l l o t h e rp r e p a r a t i o n st h e s a m e p e r c e n t a g eo f e a c h r e m a i n e di n t h es u p e r n a t e . )T h e5 ' - n u c l e o t i d a s ef r o mt h e mu s c l ec e l l s ,o n t h eo t h e rh a n d ,w a s l o c a t e dp r e d o m i n a n t l yi n a m o r e d e n s ef r a c t i o nt h a t c o n t a i n e dl i t t l et o x i no r N a + , K + - AT P a s e .T h e s p e c i f i ca c t i vi t i e s o fN a + , K + - AT P a s ea n d a - b u n g a r o

t o x i ni n f r a c t i o n sI p l u sI Iw e r e5 -t o7 - t i m e sh i g h e r t h a n t h o s ei n t h e p a r t i c u l a t eh o m o g e n a t e .O n l y t h e p a r t i c u l a t ep r o t e i nw a s a s s a y e d f o rm a r k e r - e n z y m ea c t i v i t i e st o p r e v e n t i n t e r

TA B L E2 . S p e c i f i ca c t i v i t i e so fm a r k e re n z ym e sf r o mB r d U -a n dFdU g r o z w nc u l t u r e s ,S - d a yc u l t u r e s ,a n df i b r o b l a s t s

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M u s c l e ,F dUH o m o g e n a t e 1 6 . 6 4 . 2 9 n . d . *I + I I 1 1 0 ( 6 . 6 X ) 5 . 1 0 1 1 . 3Yi e l d 2 5 . 4 5 . 0 n . d . *

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E n z y m ea c t i v i t i e sa r e e x p r e s s e da sn m o lm i n - mg o fp r o t e i n 1N u m b e r si n p a r e n t h e s e sr e f e rt o p u r i f i c a t i o no fN a + , K + - AT P ai n f r a c t i o n sI p l u sI I c o m b i n e dw i t h r e s p e c tt o t h e p a r t i c u l ah om o g e n a t e .

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f e r e n c ef r o ms o l u b l ee n z y m e ss u c ha s n o n s p e c i f i cp h o s p h a t a . 5 e s .A b o u t25% o f t h e t o t a lp r o t e i ni n t h e m o n o n u c l e a t e d m u sc l ec e l l sa n dm y o t u b e sw a s s o l u b l e ,so t h a t t h e p u r i f i c a t i o nw i t hr e s p e c tt ot o t a lc e l lp r o t e i nw a s7 -t o1 0 - f o l d .When t h e c e l l sw e r e h o m o g e n i z e di n s u c r o s e - T E A ,5 ' -

n u c l e o t i d a s ea n d T P N H - d e p e n d e n tc y t o c h r o m ec r e d u c t a s eh a d s i m i l a r d i s t r i b u t i o n so n t h e s u c r o s eg r a d i e n t .When TE Aw a s u s e d f o r t h e h o mo g en i za t i o n , h o w ev er ,t h e p a r t i c l e sc o n t a i n i n g5 ' - n u c l e o t i d a s ew e r e l e s sd e n s e t h a n t h e o n e s c o n -t a i n i n gT P N H - d e p e n d e n tc y t o c h r o m ec r e d u c t a s e ,d e m o n -s t r a t i n gt h a t t he 5 ' - n u c l e o t i d a s ei sp r o b a b l yn o t m i c r o s om a l .

P h o s p h o d i e s t e r a s eI a n d l e u c y lf - n a p h t h y l a m i d a s eh a di d e n t i c a ld i s t r i b u t i o n sb o t h i np r e l i m i n a r yc e n t r i f u g a t i o n sa n do n t h e s u c r o s eg r a d i e n t ,w h i c hs u g g e s t st h a t t h e y a r e p r e s e n ti n t h e s a m e p a r t i c l eo r p a r t i c l e s .T h e d e n s i t y d i s t r i b u t i o no ft h e s ep a r t i c l e sw a si n t e r m e d i a t eb e t w e e np a r t i c l e sc o n t a i n -i n gN a + , K + - AT P a s ea n d 5 ' - n u c l e o t i d a s e .T h i s o b s e r v a t i o ns u g g e s t se i t h e rt h a t t h e p h o s p h o d i e s t e r a s eI a n d l e u c y l, -n a p h t h y l a m i d a s ea r e p r e s e n t o n y e t a t h i r dt y p e o f p a r t i c l eo r t h a t t h e y a r e p r e s e n t i n b o t h t h e p a r t i c l e sc o n t a i n i n gN a + , K + - AT P a s ea n d t h o s e c o n t a i n i n g5 ' - n u c l e o t i d a s e .T h e s e p a r a t i o no f p l a s m a - m em b r a n ema r ke r s f r o ml i v e r

h a s b e e ne x p l a i n e do n t h e b a s i so fp l u r a l i t yo fc e l lt y p e s w i t h i nt h e t i s s u ea n d t h e h e t e r o g e n e i t yo f s u r f a c e so n a s i n g l ec e l lt y p e .I n t h e p r e s e n t s t u d y ,t h e i d e n t i c a ls e p a r a t i o n( F i g .3 )o f t h e m a r k e r si n p r e p a r a t i o n sf r o m r e l a t i v e l yh o m o g e n e o u sc u l t u r e so f m o n o n u c l e a t e dc e l l sa n d my o t u b e sr u l e so u t a ne x p l a n a t i o nb a s e d o n h e t e r o g e n e i t yo f t h e c e l lp o p u l a t i o n .We c a n n o ts a y ,h ow e v e r ,i f t h e s e p a r a t i o no fm a r k e r si s t h er e s u l to f h e t e r o g e n e i t yo f t h e c e l ls u r f a c eo r t h e a b s e n c eo f5 ' - n u c l e o t i d a s ef r o mt h i ss u r f a c e .T h ed em o n s t r a t e df e a s i b i l i t yo fp r e p a r i n gs i m i l a rm e m b r a n e

f r a c t i o n sf r o m c e l l sa t d i ff e r e n ts t a g e si n t h e i rd e v e l o pm e n ta n d t h e a v a i l a b i l i t yo fm e t h o d st o i n h i b i tt h a t d e v e l o p m e n tmake t h e i s o l a t e dp l a s m a m e m b r a n e so f c u l t u r e d mu s c l ec e l l sa n e x c e l l e n ts y s t e mf o rt h e s t u d y o fc e l lf u s i o n ,c e l l - c e l l

i n t e r a c t i o n ,a n dt h et o p o l o g yo ft h ec e l ls u r f a c e .T h i s w o r kw a s s u p p o r t e di n p a r t b y NSF G r a n tG B - 3 8 6 7 6 X ,

NI H G r a n t s 2 - R O 1 - H L 1 0 4 0 6a n d C A - 1 2 9 6 4 ,a n d a r e s e a r c h

g r a n t f r o m t h e Mu s c u l a rD y s t r o p h yA s s o c i a t i o n so f Am e r i c a .S . D . S . a n d C . K . a r e t h e r e c i p i e n t so f A m e r i c a nC a n c e rS o c i e t yP o s t d o c t o r a l F e ll o w sh i p sP F - 68 9 a n dP F - 7 8 7 ,r e s p e c t i v e l y .

1 . Kon i g s b e r g ,I . R . ( 1 96 1)C i r c u l a t i o n2 4 ,4 4 7 - 4 5 7 .2 . O ' N e i l l ,M. C . & S t o c k d a l e ,F . E . ( 1 9 7 2 )J . C e l lB i o l .5 2 ,

5 2 - 6 5 .3 . H a u s c h k a ,S .D . ( 1 9 7 2 )i nG r o wt h , N u t r i t i ona n dMe t a b o l i s m

o fC e l l si nC u l t u r e ,e d s .R o t h b l a t ,G . H . & C r i s t o f a l o ,V . J .( A c a d e m i c

P r e s s ,Ne w Yo r k ) ,

Vo l .I I ,p p . 6 7 - 1 3 0.

4 . D e P i e r r e ,J . W .& K a r n o v s k y ,M . L . ( 1 9 7 3 )J . C e l l B i o l .5 6 ,2 7 5 - 3 0 3 .

5 . B e r g , D . K . ,K e l l y ,R . B . ,S a r g e n t ,P . B . ,Wi l l i a m s o n ,P .& H a l l ,Z .W. ( 1 9 7 2 )P r o c .N a t .A c a d .S c i .USA 6 9 ,1 4 7 - 1 5 1 .

6 . Vo g e l ,Z . , S y t k ow s k i ,A . J . & N i r e n b e r g ,M. W. ( 1 9 7 2 )P r o c .N a t .A c a d .S c i .USA 6 9 ,3 1 8 0 - 3 1 8 4 .

7 . H a r t z e l l ,H . C . & F a m b r o u g h ,D . ( 1 9 7 3 )D e v e l o p .B i o l .3 0 ,1 5 3 - 1 6 5 .

8 . B i s c h o f f ,R . &H o l t z e r ,H . ( 1 9 6 8 )J . C e l lB i o l .3 6 , 1 1 1 - 1 2 7 .9 . Ya f f e ,D . ( 1 9 6 8 )P r o c .N a t .A c a d .S c i .USA 6 1 ,4 7 7 - 4 8 3 .1 0 . S t o c k d a l e ,F . , Ok a z a k i ,K . ,N am e r o f f ,M. & H o l t z e r ,H .

( 1 9 6 4 )S c i e n c e1 4 6 ,5 3 3 - 5 3 5 .1 1 . B i s c h o f f ,R . & H o l t z e r ,H . ( 1 9 7 0 )J . C e l lB io l . 4 4 ,1 3 4 - 1 5 0 .1 2 . C o l e m a n ,J . R . & C o l e m a n ,A . W. ( 1 9 6 8 )J . C e l lP h y s i o l .

7 2 ,S u p p l . 1 ,1 9 - 3 4 .1 3 . Am e s ,B . N . ( 1 9 6 6 ) i n M e t h o d si n E n z ym o l o g y ,e d s .C o l o -

w i c k ,S . P . & K a p l a n ,N . 0 . ( A c a d e m i cP r e s s ,Ne w Yo r k ) ,Vo l .V I I , p p . 1 1 5 - 1 1 8 .

1 4 . S o t t o c a s a ,G . L . , K u y l e n s t i e r n a ,B . , E r n s t e r , L . & B e r g -s t r a n d ,A . ( 1 9 6 7 ) J .C e l lB i o l .3 2 , 4 1 5 - 4 3 8 .

1 5 . To u s t e r ,O . ,A r o n s o n ,N . N . ,J r . ,Du l a n e y ,J . T . & H e n d r i c k -s o n ,H . ( 1 9 7 0 )J . C e l lB i o l .4 7 ,6 0 4 - 6 1 8 .

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1 7 . L o w r y ,0 . H . ,R o s e b r o u g h ,N . J . , F a r r ,A . L . & R a n d a l l ,R . J . ( 1 9 5 1 ) J .B i o l .C h em .1 9 3 ,2 6 5 - 2 7 5 .

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1 9 . Wa l l a c h ,D . F . H . & U l l r e y ,D . ( 1 9 6 2 )C a n c e rR e s .2 2 , 2 2 8 -2 3 4 .

2 0 . P e r d u e , J . F . & S n e i d e r ,J . ( 1 9 7 0 )B i oc hi m. B io ph ys . A c t a1 9 6 ,1 2 5 - 1 4 0 .

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C h em .3 5 1 ,1 4 2 9 - 1 4 3 4 .

Mu s c l eC e l lM e m b r a n e s 3 1 9 9