9 – AA Function

Question 1

Lysine

Answer 1

• More research done on it=seems to be the most LIMITING
• *it’s ONLY FUNCTION is a component of protein
  o Other AA have important metabolic functions
• *use it as a standard to calculate the requirement of other essential AA

Question 2

Lysine in animal nutrition

Answer 2

• First limiting AA in pigs
• Second limiting AA in poultry
• *low in grains
  o wheat/corn/barley diets MUST have supplements
• High in pulses soybean/pea
• High in canola meal
• *maybe mix a grain (low in Lys) with something high in Lys
  o Minimize the amount you need to supplement

Question 3

Methionine

Answer 3

• Contains sulfur
• First limiting AA in poultry (likely to be deficient in most of their diets)
• Second limiting AA in swine
• Can be spared by cysteine: so usually give requirement as Met + Cys
• Low in legume-based diets (ex. soybean meal)
• **important for DNA metabolism
• Precursor of taurine

Question 4

Conversion of Cys to Met

Answer 4

• NOT efficient enough to meet all the body’s Met requirement
• *it can only make 50% of Met the body requires

Question 5

Taurine

Answer 5

• Required by cats (1% by weight in diet) and salmonids
  o Conditionally essential in dogs (if diet is highly planted based)
• NOT used in protein synthesis
• No present in plants
• *important for many things

Question 6

What is taurine important for?

Answer 6

• Bile acid conjugation
• Membrane stabilization
• Modulation of intracellular Ca levels
• Important in high energy cells (Ex. heart muscle)

Question 7

Bile acid conjugation

Answer 7

• Dogs and cats: all with taurine (ie. Pooping it out)
  o Anything that increases bile acid loss=will deplete taurine (ex. high fiber diet, cat with vegan diet)
• Rats and humans: either taurine or glycine = flexibility

Question 8

What can be seen with taurine deficiency?

Answer 8

• Retinal degeneration causing blindness
• Impaired reproduction and fetal development
• Hearing loss, impaired nervous function
• Feline dilated cardiomyopathy (DCM)

Question 9

Threonine

Answer 9

• Can be deficient in animal diets
• Pulses are high in threonine
• Grains are low
• *high levels in mucous lining of small intestine
• *disproportionately high in endogenous losses (especially ruminants)

Question 10

What happens in regards to threonine with mucosal diseases?

Answer 10

• More mucous is produced=more Thr is required
• *mucin is made up of 30% Thr, but it cannot be DIGEST and REABSORBED
  o NET LOSS OF Thr

Question 11

Tryptophan

Answer 11

• 4th limiting AA in most diets
• Particularly low in CORN
• Aromatic AA (similar to phenylalanine)

Question 12

What vitamin can be synthesized from Trp (Tryptophan)

Answer 12

• B-vitamin niacin

Question 13

What is Trp a precursor for? (2)

Answer 13

• Serotonin: brain and gut function, sleep
• Melatonin: circadian rhythms

Question 14

Arginine

Answer 14

• Needed for uread cycle to break down amino nitrogen
• *carnivores have a high requirement for Arg
  o Cats and salmon
  o Can’t produce enough arginine to upregulate urea cycle after a meal

Question 15

Ile, Leu, Val: branched chain AA

Answer 15

• Major components of muscle (including smooth muscle)
• Enhance intestinal development, intestinal AA transport and mucin production
• Up-regulate innate and adaptive immune responses
• Risk of having a dietary deficiency in practical diets is LOW

Question 16

Histidine

Answer 16

• NOT required in humans, but required in all monogastric agricultural species
• *rarely deficient in diets

Question 17

What is formed by the decarboxylation of histidine? What is the role of that product?

Answer 17

• Histamine
  o Involved in immune responses (allergies)
  o Chemotaxis of WBCs
  o Vasodilation
  o Regulation of gut function (acid secretion in stomach)

Question 18

Phenylalanine

Answer 18

• Tyr can be converted to Phe
  o Tyr can more efficiently meet part or potential ALL of Phe requirement
  o BUT to be safe we assume only 50% of Phe needed can be met by Tyr
• *inability to do the conversion is a common GENETIC defect in HUMANS = phenylketonuria

Question 19

What is the name of the genetic defect in humans for the Tyr conversion to Phe?

Answer 19

• Phenylketonuria

Question 20

Aspartame

Answer 20

• Discovered by accident
• 180x sweeter than sucrose
• Must be avoided in phenylketonuria
  o Phe will accumulate in excess=neurotoxicity
• *in healthy people: metabolized to Asp, Phe and MeOH

Question 21

What are MSG and glutamate synthesized from?

Answer 21

• Glutamine (Gln): uncharged (glutamate=charged but same thing)
• *these both stimulate ‘umami’ taste receptors

Question 22

Glutamine is required in cats

Answer 22

• Involved in AA deamination when AA are used for energy
• Cats consume high proteins=need more Gln than other species
• Can synthesize it BUT NOT at an adequate rate

Question 23

Glycine

Answer 23

• Needed to synthesize uric acid
  o Birds (and reptiles): able to conserve water, but requires a lot of energy

Question 24

Synthetic AAs

Answer 24

• Can buy synthetic methionine, threonine and tryptophan
• *these 4 are usually in shortest supply in plant ingredients

Question 25

D and L AAs

Answer 25

• All AA except Gly have D and L isomers
• L-AA=natural
  o Some D-AA can be converted to L-AA (Met)
• **Synthetic Lys, Thr, Trp = L-isomers (BETTER)
  o Produced by fermentation (biological process)=from natural protein source (by living organisms)
• Synthetic Met is a mixture of D and L isomers
  o Produced by an industrial process=chemical process
  o Usually 50/50

Question 26

What are the 2 kinds of synthetic Met you can buy?

Answer 26

1. Methionine
2. Hydroxy-analogue of methionine (MHA)
   a. *Commonly used Met supplement

Question 27

Does the MHA equal the same as Met nutritionally?

Answer 27

• It is converted to Met
• Might be the same, but lots of research