biochemistry of blood, muscle and connective tissue

8/11/2019 Biochemistry of Blood, Muscle and Connective Tissue.

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LECTURE ON BIOLOGICAL CHEMISTRY FOR 2 YEAR STUDENTS

OF MEDICAL FACULTY ( 2005- 2006)

LECTURE 24

THEME: BIOCHEMISTRY OF BLOOD, MUSCLE AND CONNECTIVE

TISSUE

!LAN OF LECTURE

" B#$%$'% *+'#$+ $ ./ %$$1

2 B#$%$'% './#3 $ %$$1 '/%%

B%$$1 % 3$/#+

4 G/+/3% 1/'3##$+ $ '$++/'#7/ #*/

5 S3*'*3/ +1 *+'#$+ $ '$%%&/+

6 B#$+./# $ '$%%&/+

8 E%#+ 9 #+ 3$/#+ $ /%#' #3#%, 3*'*3/ +1 #$%$'% 3$%/

S3*'*3/ +1 *+'#$+ $ 3$/$&%'+

; S3*'*3% +1 './#'% /'*%#3##/ $ ./ *'%/.

"0 !3$/#+ $ 3'$% +1 $ $#3#%

""Mechanism of contraction and relaxation. Role of Ca2+.

"2. S$*3'/ $ /+/3& $3 *'%/


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2. Transport of nutrients to all cells of organism (glucose, amino acids, fatty

acids, vitamins, etone bodies, trace substances and others!. "ubstances such as urea,

uric acid, bilirubin and creatinine are taen away from the different organs for

ultimate excretion.

#. $egulatory or hormonal function hormones are secreted in to blood and

they are transported by blood to their target cells.

%. Thermoregulation function & an exchange of heat between tissues and blood.

'. smotic function& sustains osmotic pressure in vessels.

). *rotective function& by the phagocytic action of leucocytes and by the actions

of antibodies, the blood provides the most important defense mechanism.

+. etoxification function & neutralization of toxic substances which is

connected with their decomposition by the help of blood enzymes.

B#$%$'% './#3 $ %$$1 '/%%

Two types of blood cells can be distinguished & white and red blood cells.

-hite blood cells are called leucocytes. Their uantity in adult is %&/ x 10/.

$ed blood cells are called erythrocytes. Their uantity in peripheral blood is %,'&

' x 1012. 3esides that, there are also thrombocytes or platelets in blood.

eucocytes (white blood cells! protect an organism from microorganisms,

viruses and foreign substances, that provides the immune status of an organism.

eucocytes are divided into two groups4 5ranulocytes and agranulocytes.

5ranulocytes consist of neutrophils, eosinophils and basophils. 6granulocytes consist

of monocytes and lymphocytes.

Neutrophils

7eutrophils comprise of )0&+0 8 from all leucocytes. Their main function is to

protect organisms from microorganisms and viruses. 7eutrophils have segmented

nucleus, endoplasmic reticulum (underdeveloped! which does not contain ribosomes,

insufficient amount of mitochondria, well&developed 5olgi apparatus and hundreds of

different vesicles which contain peroxidases and hydrolases. ptimum condition for

their activity is acidic p9. There are also small vesicles which contain alalinephosphatases, lysozymes, lactopherins and proteins of cationic origin.


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5lucose is the main source of energy for neutrophils. :t is directly utilized or

converted into glycogen. /0 8 of energy is formed in glycolysis, a small amount of

glucose is converted in pentosophosphate pathway. 6ctivation of proteolysis during

phagocytosis as well as reduction of phosphatidic acid and phosphoglycerols are also

observed. The englobement is accompanied by intensifying of a glycolysis and

pentosophosphate pathway. 3ut especially intensity of absorption of oxygen for

neutrophils & so&called flashout of respiration grows. 6bsorbed oxygen is spent for

formation of its fissile forms that is carried out with participation enzymes4

1. 76*;< &=>6"? catalyzes formation of super oxide anion in reaction

2. 6n enzyme 769& =>6"? is responsible for formation of hydrogen

peroxide

#. @yeloperoxydase catalyzes formation of hypochloric acid from chloride and

hydrogen peroxide

6nion of hypochloric acid may react with the following molecule of hydrogen

peroxide and form singlet oxygen.

The active forms of oxygen show bactericidal activity and destroy microbial

nucleic acids, proteins and lipids. The leading role in bactericidal activity of

leucocytes belongs to hydrogen peroxide and hypochloride. Aormed hypochloride

produces a chlorination of frames of a microbial membrane that is accompanied by

their destruction. Byeloperoxydase with the help of hypochloride decarboxylates

amino acids.

:n the function of phagocytosis neutrophils are also assisted by leuotrienes(arachidonic acid derivatives! by means of chemotaxis stimulation.

Thus, in the phagocytosis of neutrophils participate many elements of

fermentative and non&fermentative character and with different activity mechanism.

Basophiles

3asophiles mae up 1&'8 of all blood leuocytes. They are actively formed in

the bone marrow during allergy. 3asophiles tae part in the allergic reactions, in theblood coagulation and intravascular lipolysis. They have the protein synthesis


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mechanism, which wors due to the biological oxidation energy . They synthesize the

mediators of allergic reactions histamine and serotonin, which during allergy cause

local inflammation. 9eparin, which is formed in the basophiles, prevents the blood

coagulation and activates intravascular lipoprotein lipase, which splits

triacylglycerin.

Eosinophiles

They mae up #&)8 of all leuocytes. ?osinophiles as well as neutrophiles

defend the cells from microorganisms, they contain myeloperoxidase, lysosomal

hydrolases. 6bout the relations of eosinophiles with testifies the growth of their

amount during the sensitization of organism, i.e. during bronchial asthma,

helminthiasis. They are able to pile and splits histamine, Cto dissolveD thrombus with

the participation of plasminogen and bradyinin&ininase.

Monocytes

They are formed in the bone marrow. They mae up %&E8 of all leuocytes.

6ccording to the function they are called macrophages. Tissue macrophages derive

from blood monocytes. epending on their position they are called4 in the liver

reticuloendotheliocytes, in the lungs & alveolar macrophages, in the intermediate

substance of connective tissue histocytes etc. Bonocytes are characterized by a

wide set of lysosomal enzymes with the optimum activity in the acidic condition.

The maFor functions of monocytes and macrophages are endocytosis and

phagocytosis.

Lymphocytes

The amount 20&2'8, are formed in the lymphoid tissue or thymus, play importantrole in the formation of humoral and cellular immunity. ymphocytes have powerful

system of synthesis of antibody proteins, energy is maForily pertained due to

glycolysis, rarely by aerobic way.

Thrombocytes (blood platelets)

The amount less than 18, they play the main role in the process of hemostasis.

They are formed as a result of disintegration of megaaryocytes in the bone marrow.


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Their life&time is +&/ days. :n spite of the fact that thrombocytes have no nucleus,

they are able to perform practically all functions of the cell, besides 76 synthesis.

Erythrocytes

9uman blood contains 2' trillion of erythrocytes. Their main function

transportation of 2and G2 they perform due to the fact that they contain #%8 of

hemoglobin, and per dry cells mass /'8. The total amount of hemoglobin in the

blood euals 1#0&1)0 gl. :n the process of erythropoesis the preceding cells decrease

their size. Their nuclei at the end of the process are ruined and pushed out of the cells.

/08 of glucose in the erythrocytes is decomposed in the process of glycolysis and

108 & by pentose&phosphate way. There are noted congenital defects of enzymes of

these metabolic ways of erythrocytes. uring this are usually observed hemolytic

anemia and other structural and functional erythrocytesH affections.

BLOOD !LASMA !ROTEINS

6. *rotein fractions which are received by the electrophoresis

3.

*rotein fractions which are received with the help of imunoelectropheresis on agar

gel.*rotein Goncentration6cidic I1 glycoproteid 0,20 0,%0 glI16ntitrypsyn 2,00&%,00 glGeruloplasmin 0,1'&0,)0 glGu2J 1),0,0 mmmoll9aptoglobine 1,00&%,00 glIK2& Bacroglobulin 2,'0,'0 glTranspheryn 2,'0&%,10 glAe#J 11,0&2+,0 mmmollAibrinogen 2,00&%,00 gl

Aractions Goncentration $elative contents

6lbumin #E,0 & '0,0 gl 0,'0 & 0,)0I1globulins 1,% #,0 gl 0,01 & 0,0'IK2globulins ',) /,1 gl 0,0+ & 0,1#L& globulins ',% /,1 gl 0,0/ 0,1'M globulins /,1 1%,+ gl 0,1% 0,22Total protein )',0 E', 0 gl 1,00


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:mmunoglobulins (:g!:g5 E,00&1E,00 gl:g6 1,00&%,00 gl:gB 0,)0&2,E0 gl:g 0,00&0,1' gl

:g? Till 'x10&%

6lbumin is the maFor constituent (''&)08! of plasma proteins. 9uman albumin

has comparatively low molecular weight of ''000 & +0000 and less molecular size

(1#;# nm!, than globulins and fibrinogen. *lasma albumin is synthesized in the liver

(10&1' g per day!. :ts main functions are4

1! osmotic blood pressure maintenance, thus participation in the regulation of waterdistribution between blood and inter&cellular spaceN

2! transport functionN

#! detoxification function.

?lectrophoresis separates globulins into 1&, 2&, & and &globulins. ?ach of the

fractions includes great amount of individual proteins. +'&/08 of &globulins and

'08 of &globulins are synthesized by hepatocytes. & and &globulins are transportproteins4 vitamin 6 is transported by retinol&binding protein, thyroxine thyroxine&

binding protein, transcortin is the transporter of hormones cortisol and

corticosterone, ceruloplasmin copper ions, transferin iron ions. The inhibitors of

proteolytic enzymes are alpha&1&antitrypsin, alpha&2&macroglobulin, inter&a&trypsin

inhibitor. 5lobulins haptoglobin and hemopexin prevent loss of &heme iron with

urine. 9aptoglobins (alpha&2&globulin fraction! bond with hemoglobin attenuated inthe plasma and thier complexes are pertained by reticulendothelium cells, where are

decomposed. 6nalogically hemopexin (&globulin fraction! and heme complex are

pertained by the livers. Aree iron is reutilized. & and &globulin fractions include

lipoproteins, observed in the part CipidsD. 9* or &* migrate in the

electrophoresis togrther with &globulinsN * or &* with &globulinsN O*

or pre&&* between & and &lipoproteinsN chylomicrons not move in the electric

field and stay in the start position.


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&globulin fraction contains, maForily, antibodies (immunoglobulins!. 6ntibodies

are synthesized by 3&lymphocytes. The amount of individual antibodies, different by

primary structure, is extremely big. Thus in the organism of a single man can be

synthesized up to 10+different antibodies. The structure, functions and synthesis of

antibodies are observed in the part C:mmunochemistryD.

To the fraction of antibodies belong also pathological proteins, synthesized by

myeloma by specific cells of antibodies&forming system and appear in great amount

in the plasma of the patients. "uch myeloma globulins are fragments of antibodies

and can be filtered in the idneys and secreted with urine. They are also called 3ence

Pones protein. :ts peculiarity is sediment formation in the acidic medium at '0&)0

0

Gand redissolution at higher temperature.

G/+/3% 1/'3##$+ $ '$++/'#7/ #*/

Gells are the basis units of life. Bost mammalian cells are located in tissues,

where they are surrounded by a complex extracellular matrix (ECM!, often referred

to as connective tissue. This matrix has a variety of important functions, apart from

acting as a supporting scaffolding for the cells it surrounds.?GB contains # maFor classes of biomolecules4

1. The structural proteins, collagen and elastinN

2. Gertain specialized proteins, such as fibrillin, fibronectin, and lamilin,

which have specific functions in the ?GBN

#. *roteoglycans, which consist of long chains of repeating disaccharides

(glycosaminoglycans, 565s, formerly called mucopolysaccharides! atached tospecific core proteins.

S3*'*3/ +1 *+'#$+ $ '$%%&/+.

Gollagen, the maFor component of most connective tissues, constitutes

approximately 2' 8 of the protein of mammals. :t provides an extracellular

framewor for all metazoan animals and exists in virtually every animal tissue. Bore

than 12 distinct types of collagen have been identified in mammalian tissues.?xamples of collagens types4


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type ocalization "et of polypeptide chains: "in, bones, tendon, cornea of eye,

sclera

[1(:!]2 2

:: Gartilages, vitreous body [1(::!]#

::: "in of fetus, walls of large bloodvessels

[1(:::!]#

:O basal membrane [1(:O!]#

6lthough several of these are present only in small proportions, thay may play

important roles in determining the physical properties of the tissues.

6ll collagen types have a triple helical structure. ?ach polypeptide subunit or

alpha chain is twisted into a left&handed helix of # residues per turn. Three of thesealpha chains are then wound into a right&handed super&helix, forming a rodlie

molecule 1.% nm in diameter and about #00 nm long. 6 striing characteristic of

collagen is the the occurrence of glycine residues at every third position of the triple

helical portion of the alpha chain. This is necessary because glycine is the only amino

acid small enough to be accomodated in the limited space available down the central

core of the triple helix. This repeating structure, represented as (G%->-Y!n, is anabsolute reuirement for the formation of the triple helix. -hile >and Ycan be any

other amino acids, about 100 of the >position are proline and about 100 Yposition

are hydroxyproline. 9ydroxyproline is formed by the posttranslational hydroxylation

of peptide&bound proline residues catalyzed by the enzyme prolyl hydroxylase, whose

cofactors are ascorbic acid and I&etoglutarate. ysines in the Yposition may also be

posttranslationally modified to hydroxylysine through the action of lysylhydroxylase, an enzyme with similar cofactors. "ome of these hydroxylysines may be

further modified by the addition of galactose or galactosyl&glucose through an &

glycosidic linage, a glycosylation site that is uniue to collagen.

Gollagen types that form long rodlie fibers in tissues are assembled by lateral

association of these triple helical units into a Cuarter&staggeredD alignment such that

each is displaced longitudinally from its neighbor by slightly less than one&uarter of

its length. This arrangement is responsible for the banded appearance of these fibers


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in connective tissues. Gollagen fibers are further stabilized by the formation of

covalent cross&lins, both within and between the triple helical units. These cross&

lins from through the action of lysyl oxidase, a copper&dependent enzyme that

oxidatively deaminates the Q&amino groups of certain lysine and hydroxylysine

residues, yielding reactive aldehydes. "uch aldehydes can form aldol condensation

products with other lysine& or hydroxylysine&derived aldehydes, or from "chiff bases

with the Q&amino groups of unoxidized lusines or hydroxylysines. These reactions,

after further chemical rearrangements, result in the stable, covalent cross&lins that

are important for the tensile strength of the fibers.

"everal collagen types do not form banded fibers in tissues. 6t the molecular

level, these collagens are characterized by interruptions of the triple helix with

stretches of protein lacing G%->-Y repeat seuences. These +$+-G%->-Y

seuences result in areas of globular structure interspersed in the triple helical

structure. T/ IV collagen, the best characterized example of collagens with

discontinuous triple helices, is an important component of basement membranes

where it forms a meshlie networ.

B#$+./# $ '$%%&/+.

7ewly synthesized collagen undergoes extensive posttranslational modification

before becoming part of a mature, extracellular collagen fiber. ie most secreted

proteins, collagen is synthesized on ribosomes in a precursor form, preprocollagen,

which contains a leader or signal seuence that directs the polypeptide chain into the

vesicular space of the endoplasmatic reticulum. 6s it enters the endoplasmatic

reticulum, this leader seuence is enzymatically removed. 9ydroxylation of prolineand lysine residues and glycosylation of hydroxylysines in this procollagen molecule

also tae place at this time. The procollagen molecule contains polypeptide

extensions of 20,000',000 B- at both its amino& and carboxy&terminal ends,

neither of which is present in mature collagen. 3oth extension peptides contain

cysteine residues. -hile the aminoterminal propeptide forms only intrachain disulfide

bonds, the carboxy&terminal propeptides form both intrachain and interchain disulfidebonds. Aormation of these disulfide bonds assists in the registration of the # collagen


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molecules to form the triple helix, winding from the carboxyl&terminal end. 6fter

formation of the triple helix, no further hydroxylation of proline or lysine or

glycosylation of hydroxylysines can tae place.

Aollowing secretion from the cell by way of the 5olgi apparatus, extracellular

enzymes called procollagen aminoproteinase and procollagen carboxyproteinase

remove the extension peptides at the amino& and carboxy&terminal ends, respectively.

Gleavage of these propetides may occur within crypts or folds in the cell membrane.

nce the propeptides are removed, the triple helical collagen molecules, containing

approximately 1000 amino acids per chain, spontaneously assemble into collagen

fibers. These are further stabilized by the formation of inter& and intrachain cross&

lins through the action of lysyl oxidase, as described previously.

The same cells that secrete collagen also secrete fibronectin, a large

glycoprotein present on cell surfaces, in the extracellular matrix, and in blood.

Aibronectin binds to aggregating precollagen fibers and alters the inetics of fiber

formation in the pericellular matrix. 6ssociated with fibronectin and procollagen in

this matrix are the proteoglycans heparan sulfate and chondroitin sulfate. :n fact, type

:= collagen, a minor collagen type from cartilage, contains attached proteoglycan

chains. "uch interactions may serve to regulate the formation of collagen fibers and

to determine their orientation in tissues.

E%#+ 9 #+ 3$/#+ $ /%#' #3#%, 3*'*3/ +1 #$%$'% 3$%/.

?lastin is a connective tissue protein that is responsible for properties of

extensibility and elastic recoil in tissues. 6lthough not as widespread as collagen,

elastin is present in large amounts, particularly in tissues that reuire these physicalproperties, eg, lung, large arterial blood vessels, and some elastic ligaments. "maller

uantities of elastin are also found in sin, ear cartilage, and several other tissues. :n

contrast to collagen, there appears to be only one genetic type of elastin, although

variants arise by differential processing of the hn$76 for elastin. ?lastin is

synthesized as a soluble monomer of +0,000 B- called tropoelastin. "ome of the

prolines of tropoelastin are hydroxylated to hydroxyproline by prolyl hydroxylase,although hydroxylysine and glycosylated hydroxylysine are not present. Rnlie


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collagen, tropoelastin is not synthesized in a pro& form with extension peptides.

Aurthermore, elastin does not contain repeat 5ly&=&> seuences, triple helical

structure, or carbohydrate moieties.

6fter secretion from the cell, certain lysyl residues of tropoelastin are

oxidatively deaminated to aldehydes by lysyl oxidase, the same enzyme involved in

this process in collagen. 9owever, the maFor cross&lins formed in elastin are the

desmosines, which result from the condensation of # of these lysine&derived

aldehydes with an unmodified lysine to form a tetrafunctional cross&lin uniue to

elastin. nce cross&lined in its mature, extracellular form, elastin is highly insoluble

and extremely stable and has a very low turnover rate. ?lastin exhibits a variety of

random coil conformations that permit the protein to stretch and subseuently recoil

during the performance of its physiologic functions.

S3*'*3/ +1 *+'#$+ $ 3$/$&%'+.

*roteoglycans are proteins that contain covalently lined glycosaminoglycans

(565s!. The protein bound covalently to 565s are called core proteinsN they have

proved difficult to isolate and characterize. The amount of carbohydrate in a

proteoglycan is usually much greater than is found in a glycoprotein and may

comprise up to /' 8 of its weight. There are at least + 565s4 hyaluronic acid,

chondroitin sulfate : and ::, heparin, heparan sulfate, and dermatan sulfate. 6 565 is

an unbranched polysaccharide made up of repeating disaccharides, one component of

which is always an amino sugar (hence the name 565!, either &glucosamine or &

galactosamine. The order component of the repeating disaccharides (except in the

case of eratan sulfate! is a uronic acid, either &iduronic acid (:dR6!. -ith theexception of hyaluronic acid, all the 565s contain sulfate groups, either as &esters

or as 7&sulfate (in heparin and heparan sulfate!. 9yaluronic acid affords another

exception because there is no clear evidence that it is attached covalently to protein,

as the definition of a proteoglycan given above specifies.

*roteoglycans are found in every tissue of the body, mainly in the extracellular

matrix. There they are associated with each other and some of them with collagen,another with elastin. These interactions are important in determining the structural


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organization of the matrix. :n addition, some of them interact with certain adhesive

proteins, such as fibronectin and laminin. The 565s present in the proteoglycans are

polyanions and hence bind polycations and cations such as 7a and S. This latter

ability attracts water by osmotic pressure into the extracellular matrix and contributes

to its turgor. 565s also gel at relatively low concentrations. 3ecause of the long

extended nature of the polysaccharide chain of 565s and their ability to gel, the

proteoglycans can act as sieves, restricting the passage of large macromolecules into

the extracellular matrix but allowing relatively free diffusion of small molecules.

6gain, because of their extended structures and the huge macromolecular aggregates

that they often form, they occupy a very large volume of the matrix relative to

proteins.

The + 565s named above differ from each other in a number of the following

properties4 amino sugar composition, uronic acid composition, linages between

these components, chain length of the disaccharides, presence or absence of sulfate

groups and their positions of attachment to the constituent sugars, nature of the core

proteins to which they are attached, nature of the linage to core protein, their tissue

and subcellular distribution, and their biologic functions.

H%*3$+#' A'#1:consists of an unbranched chain of repeating disaccharide

units containing 5lcR6 and 5lc76c. There is no firm evidence that it is lined to

protein, as are the other 565s. 9yaluronic acid is present in bacteria and is widely

distributed among various animals and tissues, including synovial fluid, the vitreous

body of the eye, and loose connective tissue. 6lso it present in high concentration in

embryonic tissues and is thought to play an important role in permitting cellmigration during morphogenesis and wound repair. :ts ability to attract water into the

extracellular matrix and thereby Cloosen it upD may be important in this regard. The

high concentrations of hyaluronic acid and chondroitin sulfates present in cartilage

contribute to its compressibility.

C.$+13$##+ S*%/ (Ghondroitin %&"ulfate and Ghondroitin )&"ulfate!4

proteoglycans lined to chondroitin sulfate by the =yl&"er &glycosidic bond areprominent components of cartilage. The repeating disaccharide is similar to that


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found in hyaluronic acid, containing 5lcR6 but with 5al76c replacing 5lc76c. The

5al76c is substituted with sulfate at either its % or its ) position, with approximately

one sulfate being present per disaccharide unit. ?ach chain contains some %0

disaccharide units and thus has a B- of about 20,000. Bany such chains are

attached to a single protein molecule, generating massive proteoglycans of high B-

(eg, in nasal cartilage approximately 2.'10)!. The chondroitin sulfate associate

tightly with hyaluronic acid with the aid of 2 Clin proteinsD that bind

hydrophobically to both hyaluronic acid and to the core protein, generating very large

aggregates in connective tissue. The chondroitin sulfates are located at sites of

calcification in endochondral bone. 6lso this proteoglycan is located inside certain

neurons and may provide an endoseletal structure, helping to maintain their shape.

?/3+ S*%/ I +1 II4 this substances consist of repeating 5al&5lc&7ac

disaccharide units containing sulfate attached to the ) position of 5lc76c or

occasionally of 5al. Type : is abundant in cornea, and type :: is found along with

chondroitin sulfate attached to hyaluronic acid in loose connective tissue. Types : and

:: have different attachments to protein.

H/3#+:the repeating disaccharide contains glucosamine (5lc7! and either of

the 2 uronic acids. Bost of the amino groups of the 5lc7 resirues are 7&sulfated, but

a few are acetylated. The 5lc7 also carries a G)sulfate ester. 6pproximately /0 8 of

the uronic acid residues are :dR6. :nitially, all of the uronic acids are 5lcR6, but a '&

epimerase converts approximately /0 8 of the 5lcR6 residues to :dR6 after the

polysaccharide chain is formed. The protein molecule of the heparin proteoglycan is

uniue, consisting exclusively of serine and glycine residues. 6pproximately two&thirds of the serine residues contain 565 chains, usually with an B- of '000&1'000

but occasionally much higher. 9eparin is found in the granules of mast cells and also

in liver, lung, and sin. 9eparin is an important anticoagulant. :t binds with factors :=

and =:, and also interact with plasma antitrombin :::.

H/3+ S*%/4 this molecule is present on many cell surfaces as a

proteoglycan and is extracellular. :t contains 5lc7 with fewer 7&sulfates than


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heparin, and unlie heparin, its predominant uronic acid is 5lcR6. :t plays important

role in the mediation of cell growth and cell&cell communication.

D/3+ S*%/4 this is widely distributed in animal tissues. "tructurally, it

resembles both the chondroitin sulfate and heparan sulfate. :ts structure is similar to

that of chondroitin sulfate, except that in place of a 5lcR6 in L&1,# linage to

5al76c, it contains an :dR6 in an I&1,# linage to 5al76c. Aormation of the :dR6

occurs, as in heparin and heparan sulfate, by '&epimerization of 5lcR6. 3ecause this

is regulated by the degree of sulfation, and sulfation is incomplete, dermatan sulfate

contains both :dR6&5al76c and 5lcR6&5al76c disaccharides.

S3*'*3% +1 './#'% /'*%#3##/ $ ./ *'%/.

Buscle is the maFor biochemical transducer (machine! that converts potential

(chemical! energy into inetic (mechanical! energy. Buscle, the largest single tissue

in the human body, maes up somewhat less than 2' 8 of body mass at birth, more

than %0 8 in the young adult, and somewhat less than #0 8 in the ages adult.

6n effective chemical&mechanical transducer must meet several reuirements4

1. There must exist a constant supply of chemical energy. :n vertebrate muscle,

6T* and creatine phosphate supply chemical energy.

2. There must be a means of regulating the mechanical activity ie, the speed,

duration, and force of contraction in the case of muscle.

#. The machine must be connected to an operator, a reuirement met in

biologic systems by the nervous system.

%. There must be a way of returning the machine to its original state.

Buscle is a pulling, not a pushing, machine. Therefore, a given muscle must be

antagonized by another group of muscles or another force such as gravity or elastic

recoil.

:n vertebrates, the above reuirements and the specific needs of the organisms

are met by # types of muscles4 seletal muscle, cardiac muscle, and smooth muscle.

3oth seletal and cardiac muscle appear striated upon microscopic observationN

smooth muscle is nonstriated. 6lthough seletal muscle is under voluntary nervous

control, the control of both cardiac and smooth muscle is involuntary.


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"triated muscle is composed of multinucleated muscle fiber cells surrounded

by an electrically excitable membrane, the sarcolemma. 6n individual muscle fiber

cell, which may extend the entire length of the muscle, contains a bundle of many

myofibrils arranged in parallel, embedded in intracellular fluid termed sarcoplasm.

-ithin this fluid is contained glycogen, the high&energy compounds 6T* and

phosphocreatine, and the enzymes of glycolysis.

The sarcomere is repeated along the axis of a fibril at distance of 1'00&2#00

nm. -hen the myofibril is examined by electron microscope, alternating dar and

light bands (6 bands and : bands! can be observed. The central region of the 6 band

(the 9 zone! appears less dense than the rest of the band. The : band is bisected by a

very dense and narrow U line.

-hen myofibrils are examined by electron microscopy, it appears that each

myofibril is constructed of 2 types of longitudinal filaments. ne type, the thic

filament, confined to the 6 band, contains chiefly the protein myosin. These filaments

are about 1) nm in diameter and arranged in cross section as a hexagonal array.

The other filament, the thin filament, lies in the : band and extends also into

the 6 band but not into the 9 zone of the 6 band. The thin filaments contain the

proteins actin, tropomyosin, and troponin. :n the 6 band, the thin filaments are

arranged around the thic (myosin! filaments as a secondary hexagonal array. ?ach

thin filament lies symmetrically between # thic filaments, and each thic filament is

surrounded symmetrically by ) thin filaments.

!3$/#+ $ 3'$%

Byogen group of the some glycolysis enzymes.Byoglobin chromoprotein lie hemoglobin. Gontains Ae2J, bonds to oxygen

about ' times more strongly than does hemoglobin and provides 2for oxidative

processes and aerobic glycolysis.

Byoalbumin group of lie blood albumin proteins.

!3$/#+ $ $#3#%

Bonomeric (globular! actin (5&actin! is a %#,000&B- globular protein that


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maes up 2' 8 of muscle protein by weight. 6t physiologic ionic strength and in the

presence of magnesium, 5&actin polymerizes noncovalently to form an insoluble

double helical filament called A&actin.The A&actin fiber is )&+ nm thic and has a

pitch or repeating structure every #'.' nm. 7either 5& nor A&actin exhibits any

catalytic activity.

Byosin contributes '' 8 of muscle protein by weight and forms the thic

filaments. Byosin is an asymmetric hexamer with a molecular weight of %)0,000.

The myosin has a fibrous portion consisting of 2 interwined helices, each with a

globular head portion attached at one end. The hexamer consists of one of heavy

chains and 2 pair of light chains. "eletal muscle myosin exhibits 6T*&hydrolyzing

(6T*&ase! activity and binds to A&actin, an insoluble molecule.

:n striated muscle, there are 2 other proteins that are minor in terms of their

mass but important in terms of their function. Tropomyosin is a fibrous molecule that

consists of 2 chains, alpha and beta, that attach to A&actin in the groove between its

filaments. Tropomyosin is present in all muscular and muscle&lie structures.

The troponin complex is uniue to striated muscle and consists of #

polypeptides. Troponin T (TpT! binds to tropomyosin as well as to the other 2

troponin components. Troponin : (Tp:! inhibits the A&actin&myosin interaction and

also binds to the other components of troponin. Troponin G (TpG! is a calcium&

binding polypeptide that is structurally and functionally analogous to calmodulin, an

important calcium&binding protein widely distributed in nature. Aour molecules of

calcium ion are bound per molecule of troponin G pr calmodulin, and both molecules

have a molecular weight of 1+,000.

Stromal proteins

:n seletal muscles stromal proteins presented by collagen, neuroeratin,

elastin etc.

Mechanism of contraction and relaxation. Role of Ca2+.

-hen muscle contracts, there is no change in the lengths of the thic filaments

or of the thin filaments, but 9 zone and the : bands shorten. Thus, the arrays of

interdigitating filaments must slide past one another during muscle contraction. The


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crossbridges generate and sustain the tension.

Buscle contraction consists of the cyclic attachment and detachment of the

globular head portion of myosin to the A&actin. The attachment is followed by a

change in the actin&myosin interaction, so that the actin filaments and the myosin

filaments slide past one another. The energy is supplied indirectly by 6T*.

The biochemical cycle of muscle contraction consists of ' steps4 (1! The

myosin head alone can hydrolyze 6T* to 6* J * i, but it cannot release the products

of this hydrolysis. Thus, the hydrolysis of 6T* by the myosin head alone is

stoichiometric rather than catalytic. (2! The myosin head containing 6* and *ican

rotate freely through large angles in order to locate and bind to A&actin, maing an

angle of about /0 degrees with the fiber axis. This interaction (#! promotes the

release of 6* and *ifrom the actin&myosin complex. 3ecause the conformation of

lowest energy for the actomyosin bond is %' degrees, the myosin changes its angle

from /0 degrees to about %' degrees by pulling the actin (10&1' nm! toward the

center of the sarcomere. (%! 6 new 6T* molecule binds to the myosin&A&actin

complex. Byosin&6T* has a poor affinity for actin, and thus the myosin (6T*! head

is released ('! from the A&actin. This last step is relaxation, a process clearly

dependent upon the binding of 6T* to the actin&myosin complex. The 6T* is again

hydrolyzed by the myosin head but without releasing 6* J *i, to continue the cycle.

:n resting muscle sarcoplasm, the concentration of Ga2Jis 10&+&10&E mol.

The resting state is achieved because Ga2Jis pumped into the sarcoplasmic reticulum

through the action of an active transport system, called Ga2J6T*ase, initiating

relaxation. The sarcoplasmic reticulum is a networ of fine membranous sacs. :nsidethe sarcoplasmic reticulum, Ga2Jis bound to a specific Ga2J&binding protein

designated calseuestrin. The sarcomere is surrounded by an excitable membrane (the

T tubule sustem! composed of transverse (T! channels closely associated with the

sarcoplasmic reticulum. -hen the sarcolemma (ie, the plasma membrane of the

muscle cell! is excited by a nerve impulse, the signal is transmitted into the T tubule

system and a Ga2J

release channel in the nearby sarcoplasmic reticulum opens,releasing Ga2Jfrom the sarcoplasmic reticulum into the sarcoplasm. The


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concentration of Ga2Jin the sarcoplasm rises rapidly to 10&' mol. The Ga2J&binding

sites on TpG in the thin filament are uicly occupied by Ga2J. The TpG%Ga2J

interacts with Tp: and TpT to alter their interaction with tropomyosin. 6ccordingly,

tropomyosin moves out of the way or alters the conformation of A&actin so that the

myosin head&6*&*ican interact with A&actin to start the contraction cycle.

$elaxation occurs when4

1. "arcoplasmic Ga2Jfalls below 10&+mol owing to its reseuestration into thesarcoplasmic reticulum by the Ga2J6T*aseN

2. TpG%Ga2Jloses its Ga2JN#. Troponin, via its interaction with tropomyosin, inhibits further myosin head&

A&actin interactionN

%. :n the presence of 6T*, the myosin head detaches from A&actin.Thus, Ga2Jcontrols muscle contraction by an allosteric mechanism mediated in

muscle by TpG, Tp:, TpT, tropomyosin, and A&actin.

S$*3'/ $ /+/3& $3 *'%/


19/21

twitch, glycolytic!. The type : fibers are red because they contain myoglobin and

mitochondriaN their metabolism is aerobic, and they maintain relatively sustained

contractions. The type :: fibers, lacing myoglobin and containing few mitochondria,

are white4 they derive their energy from anaerobic glycolysis and exhibit relatively

short durations of contraction.The proportion of these 2 types of fibers varies among

the muscles of the body, depending on function (eg, whether or not a muscle is

involved in sustained contraction, such as maintaining posture!. The proportion also

varies with trainingN for example, the number of type : fibers in certain leg muscles

increases in athletes training for marathons, whereas the number of type :: fibers

increases in sprinters.

!/'*%#3# $ '31#' *'%/ /$%#

Gardiac muscle also is striated. Rnlie seletal muscle, cardiac muscle exhibits

intrinsic rhytmicity, and individual myocytes communicate with each other because

of its syncytial nature. 6lso cardiac muscle has more mytochondria and less

myofibrils than seletal muscle. The T tubular system is more developed in cardiac

muscle, whereas the sarcoplasmic reticulum is less extensive and conseuently theintracellular supply of Ga2Jfor contaction is less. Gardiac muscle thus relies on

extracellular Ga2Jfor contraction. 6T* produced by oxidative phosphorilation

(aerobic glycolysis!. :n uiet (rest! conditions 100g of heart tissue uses E&10 ml 2

per minute (1' times more than other tissues!.

"ubstrates for oxidation are fatty acids, glucose, etone bodies, lactate and

pyruvate. 3ut fatty acids are the main substrate ()0&+0 8 of oxygen spent for theiroxidation!. uring wor utilization of glucose and lactate increases. actate is

produced by seletal muscle and transported by venous blood. 9eart has special

enzyme lactate dehydrogenase (51!, which transforms the lactate into pyruvate.

*yruvate used by mitochondria in oxidative decarboxylation and 6T* formed. 6lso

heart maintains the blood p9 due to this reaction.

Greatine phosphate also used in cardiac muscle and plays there double role

depo of energy and carrier of energy from mitochondria to myofibrils. 6T* produced


20/21

in mitochondria and gives the phosphate to creatine. Greatine phosphate pass through

mitochondria membrane toward cytoplasm and myofibrils. There creatine inase

removes phosphate from creatine phosphate to 6*, which produced during

contraction. 7ew 6T* formed.

B#$'./#3 $ 3#+#+&.

:n case of regular training in muscles activity of tissueHs dehydrogenases,

catalases and some other enzymes are increased. 6s a result in muscles synthesis of

glycogen, 6T*, creatin phosphate, specific muscles proteins is also increased. 6mount

of myosin increased. xidative&reductive processes are increased and most of them

are aerobic (more effective!. "o, well trained muscles can perform more hard worlonger and with less usage of energy than non&trained.

M*'%/ #@*/

Aatiue of muscles during exercise is a phenomenon that almost everyone has

experienced. -hat is its causeV The primary cause is accumulation in muscle tissue

not of lactate (due to anaerobic glycolysis! but rather of protons. This fact has been

demonstrated by infusing lactate and observing that fatiue does not necessarily

follow. :ncrease of protons (decreased p9! can affect the function of muscle in a

number of ways, including the following4

1. owering the Omaxof phosphofructoinase&1N

2. essening the release of Ga2Jfrom the sarcoplasmic reticulumN

#. essening the activity of the actomyosin 6T*aseN

%. *ossibly by affecting the conformation of some of the muscle proteins

involved in contraction.

R//3/+'/

1. Pohn -. "uttie. :ntroduction to 3iochemistry. 7ew >or4 9olt, $inehart and

-inston, :nc., 1//2.& #)% p.

2. Pohn Bc Burry, Bary ?. Gastellion. 5eneral, rganic and 3iological

Ghemistry.& 7ew Persy4 *rentice 9all, 1//2.& +)% p.


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#. $obert S. Burray, aryl S. 5ranner. 9arperHs illustrated 3iochemistry.

:ndia4 :nternational ?ducation, 200#.& )/# p.

*repared by :nna Srynytsa

$evised

6dopted at the Ghair "itting 1+.0).0'

Binutes W 12

biochemistry of blood, muscle and connective tissue

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