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Proteins/Amino Acids

Proteins/Amino Acids

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Proteins/Amino Acids

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  1. Proteins/Amino Acids

  2. Preliminary Concepts • Protein is important in building 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

  3. Roles of Protein • bulk composition (structural parts of the cell) • oxidative metabolism (used as energy source) • enzymes (regulate and influence metabolism) • plasma proteins (circulating immune bodies) • hormones

  4. Proteins within Cell Wall

  5. Elementary Composition of Proteins • Chemical composition: primarily carbon, hydrogen, oxygen • additional difference: nitrogen in amino groups (~17%) • may contain sulfur, phosphorus and iron • structure is complex

  6. Structure of Protein Molecule • Proteins are sequences of amino acids hooked together by the amino group (NH3)of one to the carboxyl group (COOH) of another called a peptide bond. • Protein chains of AA have typically 100-200 residues • Many proteins have more than one chain

  7. The Peptide Linkage

  8. Protein Structure • 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

  9. Protein Structure

  10. Amino Acids (AA) • 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

  11. Characterizing AA • Most AA are made using short-chain fatty acids (FA; such as acetic, proprionic or butyric acid) • naturally-occurring have L-configuration • synthetic have large proportion of D configs

  12. “D” vs. “L” Configuration

  13. Aliphatic Amino Acids

  14. Aromatic Amino Acids

  15. 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

  16. AA Quality • Amino acids divided into two groups: • 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

  17. Essential AA Exceptions • 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

  18. Do we need protein? • A protein requirement is really an EAA requirement (why?) • To say protein “requirement” for fish: 25-50% says nothing about requirement: it doesn’t measure intake. • Why? Variance due to culture conditions • Unfortunately, not all sources of protein are “balanced”, not all are digestible.

  19. 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

  20. Additional Protein Requirement Info • 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

  21. Requirements for Amino Acids? • 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???) • major difference is with ARG (Table 2.4, Lovell)

  22. EAA Requirements of Several Fishes, Chickens and Swine AminoChannelTilapia AcidCatfishniloticaChicken Swine ARG4.34.25.6 1.2 HIS1.51.71.4 1.2 ILE2.63.13.3 3.4 LEU3.53.45.6 3.7 LYS5.15.14.7 4.4 MET+ CYS2.33.23.3 2.3 PHE + TYR5.05.75.6 4.4 THR2.03.63.1 2.8 TRY0.51.00.9 0.8 VAL3.02.83.4 3.2

  23. Requirement for Lysine by Fish • Sciaenops ocellatus 4.43% • Oreochromis aurea 4.30% • Oncorhyncus tshawytscha 5.00% • Ictalurus punctatus 5.00% • Dicentrarchus labrax 4.82% • Morone saxatilis 3.4-4.0% • Cyprinus carpio 5.70%

  24. Sparing EAAs • 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%)

  25. EAA Requirements for Shrimp? • the quantitative requirement for only two essential amino acids has been determined for shrimp: ARG, LYS • difficulty: crustaceans are sloppy eaters, and they don’t effectively use crystalline* sources, experimental conditions allow cannibalism, extrinsic sources of EAA production too (bacteria) *Purified amino acids from bacterial culture.

  26. Crystalline Amino Acids (CAAs) • Most EAA requirement studies have used CAAs • CAAs produced by bacteria means pure! • can help reduce formulation cost of feeds because they are 99% digestible (few; 75-85% in others) • problems: reduced palatability, leaching, rapid uptake

  27. Amino Acid Metabolism: protein synthesis • Complex process occuring in most animal tissues involving 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

  28. Protein Synthesis • DNA controls formation of RNA • tRNA transfers amino acids to ribosomes • ribosomes are the source of protein synthesis (anabolism) • protein synthesis (about 50 seconds/protein) (fast!!) • amino acids also catabolized for energy • transamination or oxidative deamination

  29. 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 (APD) • APD = % of protein not rejected as feces

  30. Protein Digestibility • APD depends upon degree of purity of proteins involved • purified: gelatin, casein, soy-isolate • semi-purified: hi-pro soybean meal, glutens • practical: fish meal, squid meal, peanut meal, rice bran, etc.

  31. 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)

  32. Amino Acid Digestibility • 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

  33. 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

  34. Amino Acid Toxicity/Antagonism • 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)