Download Lecture 5: Major Nutrient Groups

Proteins/Amino Acids
Preliminary Concepts
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Protein is the principal constituent of
organs and soft structures of the animal
body
a continuous supply is needed from feed
sources throughout life for growth/repair
food protein  body protein
food protein: plant or animal
unique proteins found in each animal
no two are alike in physiological behavior
Roles of Protein
bulk composition of the body (structural
aspects of the cell)
 oxidative metabolism (used as energy source
in energy-deficient diets)
 enzymes (globular proteins that regulate and
influence metabolism)
 plasma proteins (circulating, mobile proteins
such as immune bodies)
 hormones (regulatory role)
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Proteins within Cell Wall
Special Functions
peptides (formation of proteins)
 purines/pyrimidines (control of protein
synthesis)
 histamines (active compounds, allergies)
 conjugated proteins (assist in the
excretion of other compounds)
 pigments (e.g., melanin, derived from
amino acids)
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Elementary Composition of
Proteins
Chemical composition: primarily carbon,
hydrogen, oxygen
 additional difference: contain a fairly
constant amount of nitrogen found in
amino groups (17%)
 many also contain sulfur, phosphorus and
iron
 structure is typically complex, having high
molecular weight
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Protein Classification
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simple proteins: essentially pure proteins, when
hydrolyzed, produce individual amino acids (e.g.,
egg albumin)
conjugated: protein unit linked to another nonprotein unit (e.g., casein, the protein component
of milk with phosphorus esterified to it via the
AA serine (ser)
derived: modified proteins such as peptides,
modified by heat, acidification,etc.
Conjugated Proteins
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nucleoproteins: protein + nucleic acid
(e.g., seed germs)
glycoproteins: protein + COH group (e.g.,
mucus)
phosphoproteins: protein+ P-containing
compound (e.g., casein)
hemoglobins: protein + hematin or similar
substance
lecithoproteins: protein + lecithin (e.g.,
fibrinogen)
Structure of Protein
Molecule
As mentioned, proteins are sequences of
amino acids hooked together by the amino
group of one to the carboxyl group of
another
 this bond is known as the peptide linkage
 AA found in protein are known as residues
 protein chains of AA have typically 100200 residues
 many proteins have more than one chain
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The Peptide Linkage
Protein Structure
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primary: the sequence of AA’s forming the protein
secondary: forces generated by the close proximity
of one AA residue to another (e.g.,  helix design or 
pleated sheet)(i.e., certain amino acids can form bonds
with others, if close enough, cysteine)
tertiary: bending of one AA chain due to attraction
of individual AA’s distant from each other
quaternary: packing of chains together
Protein Structure
Amino Acids (AA)
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As mentioned, proteins are polymerized
residues of amino acids
the number and proportion of AA vary
from protein to protein
when proteins are denatured, the AA
remain
to study protein, you must study AA
at least 30 different AA, some essential
others non-essential
Characterizing AA
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Most AA are derived from lower or shortchain fatty acids (FA; such as acetic,
proprionic or butyric acid)
naturally-occurring have L-configuration
synthetic have large proportion of D
configs
soluble in water, amphoteric
show various types: aliphatic, aromatic,
heterocyclic, etc.
“D” vs. “L”
Configuration
Aliphatic Amino Acids
Aromatic Amino Acids
Chemical Determination of
Protein
The direct determination of protein in
tissue is impractical due to
quantity/variation
 nitrogen, however, occurs at fairly
constant levels:
 [N] x 6.25 = protein level
 some proteins have well-known nitrogen
levels (e.g., milk @ 15.7% N)
 determined by Kjehldal N methodology
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Protein/AA Quality
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Amino acids are basically divided into two
nutritional categories:
essential: those the animal cannot synthesize
in sufficient quantity to support maximum
growth, typically dietary in nature
nonessential: synthesized by animal body,
typically non-dietary in nature
determined first by Rose (1930) working on
factorial deletion with rats
Essential AA
Exceptions
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lysine (LYS)
arginine (ARG)
methionine (MET)
histidine (HIS)
isoleucine (ILE)
leucine (LEU)
threonine (THR)
tryptophan (TRY)
phenylalanine (PHE)
valine (VAL)
ser/gly essential for chicks
pigs don’t need ARG, HIS,
LEU for maintenance
no big problem for
ruminants, why?
All essentials are in “L” form
only humans really need HIS
Protein/AA Quantitative
Requirements
A protein requirement is really an EAA
requirement (why?)
 reports persist on “protein” requirement
 protein “requirement” for fish: 25-50%
 the above statement says nothing about
requirement: it doesn’t measure intake
 unfortunately, not all sources of protein
are “balanced”, not all are digestible
 why? Variance due to culture conditions
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Factors Affecting Protein
“Requirement”
Size of fish/shrimp
 Water temperature
 Feed allowance/feeding rate
 Amount of non-protein energy sources
 Quality of protein (AA)
 Availability of extrinsic sources of nutrition
 Salinity (affects digestibility)
 Physiological/nutritional state
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Additional Protein
Requirement Info
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3 g catfish require up to 4x more protein
intake on daily basis vs. 250 g catfish
pond sources of protein are typically protein
dense (over 50% protein on DM basis)
protein “requirement” can be reduced by
feeding more frequently w/attractant
(why?)
Net Protein Utilization (NPU) for most
aquatics is around 40%
could vary with enzyme activity, molt status
in crustaceans
Requirements for Amino
Acids
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Somewhat variable due to “apparent” nature of
determinations
no standardized methodology can be applied due
to differences in feeding behavior, treatment
system design, way in which EAA is presented,
etc.
for fish, the EAA requirements are similar to
those of other animals (all similar???)
only difference is with ARG (Table 2.4, Lovell)
EAA Requirements of Several
Fishes, Chickens and Swine
Amino
Channel
Tilapia
Acid
Catfish
nilotica
Chicken
Swine
ARG
4.3
4.2
5.6
1.2
HIS
1.5
1.7
1.4
1.2
ILE
2.6
3.1
3.3
3.4
LEU
3.5
3.4
5.6
3.7
LYS
5.1
5.1
4.7
4.4
MET+ CYS
2.3
3.2
3.3
2.3
PHE + TYR
5.0
5.7
5.6
4.4
THR
2.0
3.6
3.1
2.8
TRY
0.5
1.0
0.9
0.8
VAL
3.0
2.8
3.4
3.2
Requirements for EAA
Requirement for one EAA can be
partially mitigated by a NEAA
 example: CYS sparing of MET
 CYS replaces about 60% of MET
 often reported as MET-CYS
requirement
 example: TYR sparing of PHE (about
50%)
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Requirement for Lysine by
Fish
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Sciaenops ocellatus
Oreochromis aurea
Oncorhyncus tshawytscha
Ictalurus punctatus
Dicentrarchus labrax
Morone saxatilis
Cyprinus carpio
4.43%
4.30%
5.00%
5.00%
4.82%
3.4-4.0%
5.70%
EAA Requirements by
Shrimp
the quantitative requirement for only two
essential amino acids has been determined
for shrimp: ARG, LYS
 difficulty: crustaceans are sloppy eaters,
don’t effectively use crystalline sources,
experimental conditions allow cannibalism,
extrinsic sources of EAA (bacteria)
 difficult to formulate reasonable diet and
vary only one EAA
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Crystalline Amino Acids (CAAs)
Most EAA requirement studies have
used CAAs
 CAAs produced by bacteria
 can help reduce formulation cost of
feeds because they are 99% digestible
 for most aquatics, no more than 12.5%
of AA-N
 problems: reduced palatability,
leaching, rapid uptake
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Amino Acid Metabolism:
protein synthesis
Complex process occuring in most
animal tissues
 involves DNA, RNA and ribosomes
 chromosomal DNA is storeplace of
genetic information, transmission
from one generation to the next
 DNA = 4 nucleotides: adenine,
guanine, cytosine, thymine
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Protein Synthesis
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DNA controls formation of RNA
one form of RNA (RNAt) transfers amino
acids to ribosomes
ribosomes are the source of protein synthesis
(anabolism)
protein synthesis (about 50 seconds/protein)
amino acids also catabolized for energy:
transamination or oxidative deamination
Protein Digestibility
Dietary protein quality is determined by
its bioavailability to the animal
 “bioavailability” is not simply digestibility,
it also includes assimilation and
incorporation of the AA into protein
 most common index of protein bioavailability is apparent protein digestibility
(ADP)
 ADP = % of protein not rejected as feces
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Protein Digestibility
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APD depends upon degree of purity of proteins
involved
purity ratings: purified, semi-purified,
practical
purified: gelatin, casein, soy-isolate
semi-purified: hi-pro soybean meal, glutens
practical: fish meal, squid meal, peanut meal,
rice bran, etc.
Protein Digestibility
Contrary to popular beliefs, animal
protein is not more digestible than
plant protein
 digestibility really determined by level
of purification and degree of
interaction (competition for absorption
sites) between one nutrient and another
 factors: salinity (indirect), size/age
(indirect)
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Amino Acid Digestibility
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apparent amino acid digestibility (AAAD) is
directly related to protein digestibility
proteins vary in APD, but amino acids don’t in
terms of AAAD (proteins compete with other
nutrients, AA’s don’t)
amino acids are typically absorbed in the gut
(fish) and midgut/midgut gland (shrimp)
6 transport mechanisms: 1) neutral AA’s
(mono’s), 2) basic (diamino’s), 3) acidic
(dicarboxylic’s), 4) aromatics, 5) alanine and 6)
glycine
Amino Acid Assimilation
“assimilation” is not transport, it
involves the appearance of AA’s in
various tissues (blood, hemolymph,
muscle, etc.)
 appearance OK for intact-sourced AA’s,
but rapid and unsynchronized for CAA’s
(too much, too quickly)
 CAA’s possibly used with increased
feeding frequency
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Amino Acid Toxicity/Antagonism
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Toxicity/antagonisms are result of dietary
imbalances in EAA
when one EAA is fed in excess it can also
increase the requirement for another,
structurally-similar EAA
toxicity = overfeeding of one EAA and negative
effects not mitigated by increasing other EAA
antagonism = one EAA regulates uptake of
another
LEU/ILE in catfish (Robinson, 1984)
LYS/ARG in shrimp (Fox, 1992)