protein digestion and absorption
TRANSCRIPT
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Protein Digestion and Absorption
Dietary proteins, with few exceptions, are
not absorbed.
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Protein Digestion and Absorption
Dietary proteins, with few exceptions, are
not absorbed.
They must be digested first into amino acids
or di- and tri-peptides.
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Protein Digestion and Absorption
Dietary proteins, with few exceptions, arenot absorbed.
They must be digested first into amino acidsor di- and tri-peptides.
Through the action of gastric and pancreatic
proteases, proteins are digested within thelumen into medium and small peptides
(oligopeptides.
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Digestion of protein - hydrolysis
R CH C
O
COOHCH
R
N
HNH2
R CH
NH2
C
O
OHCOOHCH
R
HHN
+H2O+ proteases
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Protein digestion begins in stomach
Pepsin - inactive precursor pepsinogen
ctive ! pH 2-"# inactive pH$%
&ecretion stimulated by acetylcholine or
acid
Only protease 'hich can brea( do'n
collagen
ction terminated by neutralisation by
bicarbonate in duodenum)
N)*) ll proteases stomach , pancreatic secreted as
inactive precursors) .ost protein digestion occurs in the
duodenum/0e0unum
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ctivation of pancreatic proteases
1rypsinogen 1rypsin
ntero(inase
1rypsinogen
Chymotrypsinogen
ProelastaseProcarbo3ypeptidase
1rypsin
Chymotrypsin
lastaseCarbo3ypeptidase
ctive proteases inactivated by trypsin
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peptidases
aminopolypeptidasetransporters
amino acidsDi/tripeptides
Cytoplasmic peptidase
transporters
mino acids
Protein
peptides
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Pancreatic en4ymes
ssential for digestion essential for life
Proteases
5nactive form
ctivated in gut
cinar cells
6ipases mylases
ctive en4ymes
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Pancreatic !n"ymes
The bul# of protein
digestion occurs within
the intestine due to theaction of pancreatic
proteases.
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Pancreatic Proteases
The two primary pancreatic proteases are
trypsin and chymotrypsin.
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Pancreatic Proteases
The two primary pancreatic proteases are trypsinand chymotrypsin.
They are synthesi"ed and pac#aged withinsecretory $esicles as inacti$e proen"ymes%
trypsinogen chymotrypsin
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Pancreatic Proteases
The two primary pancreatic proteases are trypsin andchymotrypsin.
They are synthesi"ed and pac#aged within secretory $esiclesas inacti$e proen"ymes%
trypsinogen chymotrypsin
The secretory $esicles also contain a trypsin inhibitor to ser$eas a safeguard against trypsinogen con$erted to trypsin.
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&ther Pancreatic Proteases
Procarboxypeptidasecarboxypeptidase
Proelastase elastase
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Trypsin
Trypsinogen is con$erted to trypsin by the
en"yme entero#inase (enteropeptidase
secreted by cells lining duodenum.
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Trypsin
Trypsinogen is con$erted to trypsin by the
en"yme entero#inase (enteropeptidase
secreted by cells lining duodenum. Trypsin then acti$ates the con$ersion of
other "ymogens from their inacti$e to acti$e
forms.
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Trypsin
Trypsinogen is con$erted to trypsin by theen"yme entero#inase (enteropeptidase
secreted by cells lining duodenum. Trypsin then acti$ates the con$ersion of
other "ymogens from their inacti$e to acti$eforms.
'nhibition of trypsin will slow acti$ation ofother proteases.
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Trypsin contd
Trypsin cataly"es the splitting of peptide
bonds on the carboxyl side of lysine and
arginine residues. 't has a p) optimum of *.+ to . (al#aline.
lassified as a serine protease (serine and
histidine at the acti$e site.
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Trypsin, hymotrypsin
/imilar chemical compositions
hief differences are specificity of action%
trypsin 0 lysine, arginine
chymotrypsin 0 tyrosine, phenylalanine, tryptophan,methionine,leucine
(aromatic or large hydrophobic side chains
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1oc# and 2ey 3odel of
!n"yme Acti$ity
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4isuali"ation of the 1oc# and
2ey 3odel of !n"yme 5unction
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1oc# 2ey !n"yme atalysis
The 6Acti$e /ite7 contains%
A shape that fits a specific substrate(s
/ide chains that attract (chemically thesubstrate
/ide chains that are positioned to speed thereaction
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!n"yme atalysis
-&) of serine 89:
attac#s ;& of peptide
bond. )istidine :*donates a proton to the
< of the peptide bond
leading to clea$age
and acylation of theen"yme. Asp-8= is
also in$ol$ed.
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arboxypeptidase
&&- terminal peptide bond )ydrolysis occurs most readily if the &&-
terminal residue has an aromatic or bul#y
aliphatic side chain. >inding of a typical substrate results in a
rearrangement of the acti$e site (induce fit.
?lutamate-=*, Arginine-8@:, Arginine-8=*,Tyrosine-=@ are important at the acti$e site.
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arboxypeptidase
) ) & ) &
' ' '' ' ''
< - - - < - -
' ' ' '
B ) )= &
' AB&3AT'
/'D! )A'owman->ir# inhibitor
>oth are inacti$ated during moist heat
treatment.
Protease inhibitors are proteins which bind
to the en"yme, rendering them inacti$e.
/ymptoms include pancreatic hypertrophy
due to stimulated secretory acti$ity.
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bsorption of peptides and amino acids
1ransport at the brush border7) ctive transport by carrier)
2) .ostly dependent on Na+ gradient - co-transport
similar to that for glucose
") &ome amino acids basic# and neutral 'ith
hydrophobic side chains are absorbed by facilitated
diffusion
Protein assimilation affected by -
Pancreatitis# congenital protease deficiencies#
deficiencies of specific transporters
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Absorption of Amino Acids
The transporters bind amino acids only after
binding sodium.
The fully loaded transporter undergoes aconformational change that dumps
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Absorption of Amino Acids
Absorption of amino acids is dependent on
the electrochemical gradient of
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Absorption of Peptides
There is $irtually no absorption of peptides
longer than three amino acids but there is
abundant absorption of di- and tri-peptides,probably by a single transport molecule.
The $ast bul# of di- and tri-peptides are
digested into amino acids by cytoplasmicpeptidases.
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Absorption of 'ntact Proteins
Absorption of intact proteins occurs rarely.
4ery few proteins can get through the
gauntlet of soluble (lumen and membrane-bound proteases intact.
6
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Absorption of 'ntact Proteins
/hortly after birth, neonates can absorb
intact proteins.
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Absorption of 'ntact Proteins
/hortly after birth, neonates can absorb
intact proteins.
3ost of these intact proteins areimmunoglobulins which can be absorbed
from the $ery first mil# (colostrum and this
imparts early neonatal passi$e immunity.
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Absorption of 'ntact Proteins
/hortly after birth, neonates can absorbintact proteins.
3ost of these intact proteins areimmunoglobulins which can be absorbedfrom the $ery first mil# (colostrum and thisimparts early neonatal passi$e immunity.
6losure7 is when the small intestine losesthe capacity to absorb intact proteins.
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Protein BeFuirements
3aintenance ; nutritional reFuirements to
stay ali$e (does not reFuire positi$e >G
gain
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Protein BeFuirements
3aintenance ; nutritional reFuirements to
stay ali$e (does not reFuire positi$e >G
gain
?rowth ; positi$e tissue accretion
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Protein BeFuirements
3aintenance ; nutritional reFuirements to stay
ali$e (does not reFuire positi$e >G gain
?rowth ; positi$e tissue accretion
Beproduction ; tissue specific growth related toreproduction, reproducti$e function (mil#, eggs,
reproducti$e tissue
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Protein Re8uirements
0
10
20
30
40
50
60
1 3 5 7 911
13
15
17
19
21
23
25
27
ge
1issue9ro'th
Intestine
Muscle
Reproduction
Maintenance
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)ow do you express a protein
reFuirement H Protein percent of the diet
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)ow do you express a protein
reFuirement H Protein percent of the diet
Amino acid percent of the diet
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?rowth Gill Dictate 5eed 'nta#e
Body Wt
0
24
6
8
10
12
14
16
18
20
1 2 3 4 5 6 7 8
ge
Body Wt
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'nta#e Gill Dictate Actual BeFuirement
0
5
10
15
20
25
1 2 3 4 5 6 7 8
ge
Dietary: % rotein
% !"ino !cid
Body Wt
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)ow do you express a protein
reFuirement H Protein percent of the diet
Amino acid percent of the diet
Amino acid percent of total protein
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)ow do you express a protein
reFuirement H Protein percent of the diet
Amino acid percent of the diet
Amino acid percent of total protein
Digestible protein percent of the diet
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Digestible Protein !stimates
Digestible protein ; inta#e 0 output
(amino acids
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Digestible Protein !stimates
Digestible protein ; inta#e 0 output
(amino acids
Diet formulated to .9I T/AA
(methionine cystine
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Digestible Protein !stimates
Digestible protein ; inta#e 0 output
(amino acids
Diet formulated to .9I T/AA
(methionine cystine
5eathermeal ; *I digestible methionine
5ishmeal ; 9I digestible methionine
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Digestible Protein !stimates
Digestible protein ; inta#e 0 output
(amino acids
'ntestinal microbes will modify amino acid
composition of digesta
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Digestible Protein !stimates
Digestible protein ; inta#e 0 output
(amino acids
'ntestinal microbes will modify amino acid compositionof digesta
!xcreta will reflect microbial as well as de no$o dietaryamino acid a$ailability
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Digestible Amino Acid !stimates
eacectomi"ed roosters 0 precision feeding
- total excreta collection, amino acid
determination
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Digestible Amino Acid !stimates
eacectomi"ed roosters 0 precision feeding,
ollect all excreta,amino acid determination
'leal Digesta 0 collect digesta from terminal
small intestine, non-digestible dietary
mar#er (cannula for pigs, terminalcollection for poultry
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Digestible Amino Acid Determination
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Digestible Amino Acid Determination
I Digestibility ;
AA J A'A (feed 0 AAJA'A (digesta
KKKKKKKKKKKKKKKKKKKKKKKKKKKKKK
AA J A'A (feed
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Digestible Amino Acid Determination
I Digestibility ;
A'A ; 8.:I feed, @.I digesta
methionine ; .:I feed, .=:I digesta
I A$. 3eth ; .:J8.: - .=:J@.
.:J8.:
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Digestible Amino Acid Determination
I Digestibility ;
A'A ; 8.:I feed, @.I digesta
methionine ; .:I feed, .=:I digesta
I A$. 3eth ; .:J8.: - .=:J@. ; .LL - .+=:
.:J8.: .LL
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Digestible Amino Acid Determination
I Digestibility ;
A'A ; 8.:I feed, @.I digesta
methionine ; .:I feed, .=:I digesta
I A$. 3eth ; .:J8.: - .=:J@. ; .LL - .+=:
.:J8.: .LL
8I Digestible 3ethionine
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)ow do you express a protein
reFuirement H Protein percent of the diet
Amino acid percent of the diet
Amino acid percent of total protein
Digestible protein percent of the diet
'deal Protein ratios (relationships among
amino acids
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)ow do you express a protein
reFuirement H Protein percent of the diet
Amino acid percent of the diet
Amino acid percent of total protein
Digestible protein percent of the diet
'deal Protein ratios (relationships among
amino acids
Protein or amino acid inta#eJday (gms
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9ro'th Response to 6ysine
00#2
0#4
0#6
0#81
1#2
1#4
1 2 3 4 5 6 7 8 9 10 11
*ody ;t
6ysine
0
50
100
150
200
9ro'th
$ysine
Body Wt
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0
20
40
60
80
100
120
140
160
180
1 2 3 4 5 6 7 8 9 10 11
0
5
10
15
20
25
Body Wt
Breast Wt
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Carcass Development
0
20
40
60
80
100
120
140
1 3 5 7 911
13
15
17
19
21
23
9e
Relative9ro'th s%eleton
"uscle
&at
Protein Re8uirements
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Protein Re8uirements
0
10
20
30
40
50
60
1 3 5 7 911
13
15
17
19
21
23
25
27
ge
1issue
9ro'th
Intestine
Muscle
Reproduction
Maintenance
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!conomics of Protein
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!conomics of Protein
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aloric cost of protein deposition
There is a genetic limit to protein accretion.
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aloric cost of protein deposition
There is a genetic limit to protein accretion.
The goal is to maximi"e muscle accretion
without feeding protein as an energy source.
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aloric cost of protein deposition
There is a genetic limit to protein accretion.
The goal is to maximi"e muscle accretion
without feeding protein as an energy source.
arbohydrate ; ,),& (@ calories
5at ; ,) (9 calories
Protein ; ,),< (@ calories
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aloric cost of protein deposition
>alancing diets, research and real world
5or a gi$en set of growing conditions, there
is an energetic mix of caloric sources that is
optimum
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aloric cost of protein deposition
5or a gi$en number of calories consumed%
on$erting protein to energy is
energetically inefficient and results inmetabolic heat production
(en$ironmental considerations
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aloric cost of protein deposition
5or a gi$en number of calories consumed%
!xcess calories relati$e to the animals
genetic capacity to synthesi"e protein will
increase carcass fat deposition (%P ratio
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aloric cost of protein deposition
oncept of caloric density%
Ghat is the proportion of total calories
coming from protein, fat, carbohydrate.
'socaloric diets - high fat, low fat
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Amino Acid >alance
)ow would an optimum balance of amino
acids be defined H
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Amino Acid >alance
)ow would an optimum balance of amino
acids be defined.
This Fuestion is outcome dependent.
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Amino Acid >alance
)ow would an amino
acid optimum be
defined H
&rder of limitation
influencing growth.
Diets selected amino
acids. 0
20
40
60
80
100
120
140
160
180
1 2 3 4 5 6 7 8 9 10 11
0
5
10
15
20
25
Body Wt
Breast Wt
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Amino Acid >alance
)ow would an aminoacid optimum bedefined H
&rder of limitationinfluencing growth.
omposition ofcarcass protein depots.
0
20
40
60
80
100
120
140
160
180
1 2 3 4 5 6 7 8 9 10 11
0
5
10
15
20
25
Body Wt
Breast Wt
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Amino Acid >alance
3inimi"ing ammonia production (alance
3inimi"ing ammonia production (G loss by P treatment ; + gms
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ommercial Application of P!B
/ome companies will use the P!B assay in
Fuality control assays for incoming
ingredients.
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ommercial Application of P!B
/ome companies will use the P!B assay inFuality control assays for incomingingredients.
These assays will often incorporate chic#sand utili"e one le$el of P, usually +I or9I.
'A3/ uses this assay to monitor theirincoming poultry byproduct meal.