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Chapter 9
Protein and Amino Acids
• Protein vary widely in chemical composition,
physical property, size shape, solubility,
biological function.
General structure of amino acid
NH2
O
R —— C ——C
OH
OH
• R is the remainder of the molecule
attached to the C atom associated with the
α-amino group of the amino acid.
• Amino acids not synthesized in animal
tissues of most specie in sufficient
amounts to meet are termed essential or
indispensable, whereas those generally
not needed in the diet because of
adequate tissue synthesis are termed
nonessential or dispensable.
Essential
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Arginine
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalnine
Threonine
Tryptophen
Valine
Nonessential
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Alanine
Aspartic acid
Citrulline
Cystine
Glutamic acid
Glycine
Hydroxyproline
Proline
Serine
tyrosine
• Arginine: is required for some species for
maximum growth, adult do not require.
However dog, cat show severe sign of
deficiency.
• Glutamine: is a dispensable, 但生病時, 是
唯持正常代謝所需，是indispensable.
• In most animal:
• in mucosa : glutamate＋proline合成
ornithine ，ornithine轉成citrulline，再送至
腎臟產生arginine( urea cycle)
• In cat、 dog: ornithine→citrulline與
citrulline→arginine未能進行，∴arginine is
essential。在higher protein ，缺arginine
無法進行urea cycle，引起hyperammonia
• Taurine :
1. Synthesized by most mammals from methionine
and cysteine
2. It is indispensable for cat only.
3. a amino sulfonic acid, occurs as a free amino acid.
is not present in protein
4. develop degeneration of retina of the
eye.(myocardium and retina contain high
concentration of free taurine)
5. Taurine deficiency occurred in the low dietary
sulfer-containing amino acids
•
Methionine→ cysteine→
cysteine sulphinic acid →hypotaurine
→taurine
Structure of protein
1. Primary structure = linkage between α-carboxyl
of one amino acid group of another (peptide
linkage)
R
O H
R1 O
H2N C
C N
C
H
H
C
OH
2. Secondary structure = polypeptide in the
form of a α-helix by means of hydrogen
bond CO—HN. α—helix or β—pleated
sheet, supercoil
3.Tertiary structure :
polypeptide into a globular form by means of:
1.
2.
3.
4.
hydrophobic
disulfide linkage (s-s)
salt bridge
hydrogen bonding
a globular form
4. Quaternary structure
alignment of several tertiary structure
into one protein by means of hydrogen
bonds, electrostatic, salt bonds
Ex: hemoglobin consist of four single strand
tertiary.
• Gastrointestinal microflora synthesize
protein from nonprotein N sources.
• The length of the chain and the order of
arrangement of amino acids within the chain
are two of the main factors determining the
characteristics of the protein.
• Synthesis of protein from amino acids. The
linkage between amino acids called
peptide bond. Elongation of chain from
tripeptide, polypeptide.
• All naturally occuring amino acid are in the
L-form. which is the biologically active
form. (但合成大多為L與D form的混合物).
• All proteins can be classified on the basis
of their shape; their solubilities in water,
salt, acids, bases and alcohol; and other
special characteristics.
• Egg albumin is the most perfect protein for
meeting animal need because of its nearly
ideal amino acid composition and its high
digestibility.
• Corn endosperm: Zein(玉米蛋白) is low in
lysine and tryptophan. Opaque-2 corn is
lower contain in zein, 此種玉米含較高量之
lysine及tryptophan.
• A sensitive measure of the nutritive value of
protein is the balance among its essential
balance, no two protin have an identical amino
acid composition.
A.
Globular protein球狀蛋白
Albumin
Globulin
Glutelin
Prolamines
Histone
Protamine
B.
Fibrous protein
Collagens
Elastins
Keratin
C.
Conjugated protein
Lipoprotein
• Represented by the menbrane proteins of
animal cells.
• myelin: in nervous system mucolipid
erythrocyte membrane
• The protein content of plasma lipoprotein
ranges from 2% in chylomicron to about
50% in high density lipoprotein.
Glycoprotein
• Chondroitin sulfate A. B. C. (protein
complex of sulfated polysaccharides)出現
在cartilage, tendon and skin.
• Mucoprotein: complex of protein with:
– amino sugar (glucosamine, galactosamine.)
– hexose, manose, galactose.
– pentose, fucose
– sialic acid
Glycoprotein
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serum cholinesterase
gonadotrophin(性腺素)
mucous secretion
ovalbumin (mucoprotein containing
glucosamine, mannose).
• ovomucoid (containing hexosamine, hexose;
trypsin inhibitor in egg white)
• aspartic acid (是主要與醣類結合之胺基酸)
Functions
• Present as components of cell membrane,
muscle, skin, hair, hooves, blood plasma
protein, enzyme, hormones, immune
antibody.
Tissue protein
1. Collagen: triple helix, 含proline,
hydroxylproline
2. Elastin: resemble denatured collagen and
consist of long, randomly ordered, ploy-peptide
chain. minor component of musculature.
3. myofibrilar protein : the proteins of
sacroplasm.(肌肉與稀鹽類均質後可萃取﹐含有
20種酵素)
4. contractile protein : three protein- actin,
tropomyosin B and myosin. 與muscle
contraction有關.
Tissue protein
5. Keratins : proteins of hair, wool, feathers,
hooves, horns, claws, beaks.
6. Blood proteins : albumin and a series of
globulins, apoprotein
7. Enzymes : hydrolytic and degradative
metabolic and synthetic reaction.
8. Hormones : insulin, growth hormone,
gonadotrophic hormone, parathyroid
hormone and calcitonin。
Metabolically active peptides and
polypeptides
• A large number of peptides and polypeptide been identified in modulating
growth and other metabolic activity.
• such as
–
–
–
–
insulin-like growth factor (IGF-1,)
transforming growth factor beta (TGF-B)
fibroblast growth factor (FGF)
nerve growth factor (NGF)
Metabolism
• two phases: catabolism (degradation) and
anabolism (synthesis)
• The conversion of dietary protein to tissue protein
involves:
1. Intact dietary protein
hydrolysis in GI tract (catabolism)
2. Amino acid in intestinal lumen
absorption from GI tract
3. Amino acid in blood
synthesis in tissues (anabolism)
4. Intact tissue proteins
• Even protein hydrolyzed easily in the GI
tract do not have a high nutritional value, if
they have a deficiency or an unbalance of
one or more amino acids.
• Dietary protein not containing the
proportion of essential amino acids to
meet the animal needs cannot be used
efficiently for tissue protein synthesis.
Digestion
• Protein→→→ tripeptide, dipeptide, amino
acid( lumen) → absorption → brush border
enzyme (dipeptidase, tripeptidase) →
dipeptidase, tripeptidase in enterocycte
→ amino acids
Hydrolysis determine the degree of
absorption of amino acid
(A) Digestible protein refer to that disappearing
from the ingesta as it passes down the GI
tract.
– Nitrogen in feces include:
1. Unabsorbed dietary N .
2. Metabolic fecal N
Metabolic fecal N :
1.Normal metabolism of tissue protein cells
2.sloughed residue of digestive enzyme.
3.other substrate secreted into the lumen.
(B) After absorption, amino acid are subject
to further losses in utilization through
metabolism in the liver and other tissues.
losses N mainly as urinary urea N
(mammal), or uric acid (bird).
(C) The degree of utilization of feed protein
depend on
1. digestibility, absorbability
2. utilization of its component amino acids
after absorption.
Absorption of amino acids
1. early postnatal life:
– absorbed by pinocytosis. (如immune globulins and
lactoferrin)
2. postnatal life:
– absorbed by active transport ( two system )
• one for neutral amino acid.
• one for basic amino acid.
– 相關性質之amino acid由於競爭carrier, 吸收會受抑制。
如leucine與 isoleucine methionine與lysine.
3. peptide are absorbed directly from the rumen
and omasum
Fate of amino acids after
absorption
1. tissue protein synthesis
2. synthesis enzyme, hormone and
metabolites
3. deamination or transamination and use of
the carbon skeleton for energy.
• Amino acid in the GI have three source:
• 1.Dietary ingestion
• 2.recycle from other nitrogen
substance( digestive enzyme, sloughed
mucosa cell)
• 3.synthesized by microorganism
A. Synthesis by microorganism
• Bacteria, protozoans can synthesis all
amino acids in presence of ammonia, S,
carbon sources
• Rumen, large intestine
• In ruminant, synthesis amino acid from
nonprotein nitrogen.
B. Body tissue
Tissue synthesis and degradation of amino
acid in animal. Muscle, liver, brain, adipose
tissue and others…..
Sites of amino acid degradation
• Microbes, cell and tissue specific
pathways degrade all amino acids,
• Liver is the principle organ, and small
intestinal cells to process of degradation.
• Transamination, decarboxylation,
hydroxylation .
• Product of degradation: amionia, S, fatty
acids (VFA). CO2
Nitrogen cycling in the intestine
• Dietary nitrogen→intestine →blood
• Endogenous N (urea) →intestinal lumen
→microbial action →NH3 →used for
incorporation into amino acids to produce
microbial protein →digested by host
NO in animal nutrition and health
• Nitric oxide is a mediator of immune function, a
neurotransmitter, a signaling molecule, and
endothelium-derived relaxing factor and other
positive role in metabolism.
• It is a cytotoxic free radical.
• Is synthesized from arginine through action of
the enzyme nitric oxide synthase (NOS).
• Many nutrient, including protein and amino acid
may modulate NO production by NOS.
Ruminant nitrogen metabolism
• RUP: rumen undegraded protein
Synthesis of protein
DNA (chromosomal component of cell)
│ carry the genetic information
↓
transcript into a strand of messenger RNA
↓
tranlation of mRNA into protein
Whole body protein turnover
• Is a dynamic process involving continuous
and simultaneous protein synthesis and
protein degradation.
• Each organ or tissue has its own rate of
protein turnover.
• The rate of body muscle growth is affected
by the rate of protein synthesis relative to
degradation.
Deamination and Transamination
• Deamination :removal of the amino group
from carbon of amino acid and entrance
of the amino group into the urea.
• Transamination: transfer an amino group
from one amino acid to the carbon of a
keto acid.
Urea cycle
• The urea or ornithine cycle is a key metabolic
phenomenon in protein metabolism.
• Uric acid is end product of purine metabolism
in human and other primate, in other
mammals the principal end product is the
oxidation product of uric acid, allantoin.
Protein and amino acid
requirement and deficiency
1. Nonruminant (pig, chichken, human)
require essential amino acid.
2. Nonruminant herbivores, and adult
ruminant depend on nonprotein N and
synthesize protein or amino acid.
3. Adult ruminant (cattle, sheep) can depend
entirely on nonprotein N in the diet by
virtue of their rumen microbes.
•
•
Because most energy sources are low in
protein and protein supplement are
expensive, so inadequate protein is the
most common.
protein is diverted to energy only when it
is provide in excess of the metabolic
requirement or calorie intake is
insufficient.
sign of protein deficiency
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anorexia,
reduced growth rate
negative N balance
reduced feed
efficiency
• reduced serum
protein concentration
• anemia
• fat accumulation in
the liver
• edema
• reduced birth weight
• reduced milk
production
• reduced enzyme,
hormone synthesis
• Individual amino acid deficiency result in
deamination of the remaining amino acids,
loss of NH3 as urea, and use of the carbon
chain for energy.
• Ex: tryptophan deficiency : eye cataracts.
threonine, methionine : fatty liver
lysine (in bird)
: abnormal
feathering
• individual feedstuffs are inadequate amino
acid
• Ex: corn: lysine, tryptophane,
SBM: rich in lysine, tryptophan,
deficient in methionine-cystine.
seasame meal: inadequate lysine
• first limit amino acid: lysine
• second and third limit amino acid:
threonine, tryptophan
D-amino acid and nonprotein N
• Natural: L-form.
• D-form amino acid used inefficiency.
(except of methionine).
• Nonprotein nitrogen (NPN)
=diamonium citrate, Urea, amino acid,
peptide, amines, amide and nucleic acid
(存於forage).
• The efficiency of utilization of NPN
compounds depend on
1. solubility of the NPN.
2. availability to the microflora of readily
available carbohydrate.
Antagonism
• growth depression can be overcome by
supplementation with an amino acids
structurally similar to the antagonist
• Ex: lysine and Arginine. (structure similar)
• Excess of lysine→ growth depress
→improve by addition of arginine
• Antagonist differ from imbalance of amino
acids
Toxicity
• adverse effect of an amino acid in excess
cannot be overcome by supplementation
with another amino acid
• Ex: Methionine
Imbalance
• proportion of dietary amino acids that has
an adverse effect presentable by a
relatively small amount of the most limiting
amino acid.
• animals will reject the imbalanced diet, but
will support life.
protein-free-diet will be consumed largely,
but not support life.
Excessive protein intake
• Depression in weight gain, feed intake.
Hair dull and coarse.
• Ammonia toxicity (urea excessive)
Measure of nutritive value of
proteins
1. Biological value (BV) =
N intake - ( fecal N + urinary N )
N intake - fecal N
x100%
• BV is defined as that percentage of N absorbed
from the GI tract is available for productive body
function.
• estimate of the efficiency of use of the absorbed
protein for combined maintenance and growth.
2. protein efficiency ratio (PER) =
body weight gain (g)
protein consumed (g)
3. Net protein Utilization (NPU) =
(
body N with
body N with
) – (
)
test protein
protein-free diet
x100%
total N intake
4. Net protein value (NPV) =
BV × digestion coefficient.
5. Assay of free amino acid concentration
of blood plasma :
• changing in amino acid patterns following
ingestion of the test protein.
6. Blood urea N:
• At level of dietary protein either above or
below the requirement or with diet
deficient or imbalanced in one or more
amino acid, blood urea N is elevated.
(serum urea fit well)
• All of the estimates of protein utilization
described have their limitations and no
one estimate is superior to all others under
all conditions.
• PER is the best estimate of protein value
for growth.
Biological availability of amino
acids
1. microbiological assay :
• test material is digested by enzyme, acid
or alkaline hydrolysis, and the amino acid
composition of hydrolysate is determined
by microbiological assay
• the rate and degree of release of amino
acid is taken as an index of the availability
to the animal.
2. fecal analysis
• Amino acid availability (%) =
AA total － ( TFAA protein － TFAA protein-free )
AA total
3. analysis of terminal ileum content :
• absorption of amino acid from the large
intestine and degree of degradation in the
lower intestine ileum are not defined well.
• amino acid content of ileum contents can
be used to calculate the availability of
individual amino acid.
4. growth assay :
• comparing the growth curve of animals fed
the test protein with that of animals fed the
amino acid diet containing the amino acids
of concern.
• Estimate the proportion of amino acid in
the test protein utilized for growth.
5. plasma free amino acids :
• The change in relative concentration of
amino acids in the plasma following a
meal of the test protein.
• The duration of fasting and the selection of
appropriate intervals for blood sampling
are important.
• Processing methods including grinding,
pellecting, drying, oil extraction, and
heating.
• The greatest single factor affecting amino
acid availability from feedstuffs is proper
heating of feedstuffs during processing.
• application of heat must be a balance
between beneficial and destructive effects.
• destruct or delayed release during
digestion owing to change in linkage
between amino acids and other
components.