Amino Acid Function Flashcards
Importance of protein
- Only functions as a component of protein synthesis… making it the most limiting
- Used as a standard for calculating the requirements of other essential amino acids
Lysine as a limiting amino acid
First limiting amino acid in pigs
Second limiting amino acid in poultry
Lysine presence in food
- low in grains (will need to be supplemented)
-high in pulses soybean/pea
-high in canola meal
Methionine
Contains sulfur
*first limiting amino acid in poultry, second limiting in swine
Importance of methionine
Needed for DNA metabolism and is a precursor of taurine
What diets is methionine and cysteine low in?
Low in legume-based diets
*soybean is higher but still considered low
How can methionine be metabolized?
Can be spared by cysteine so usually give requirement as Met +Cys
**this conversion is not efficient enough to meet all of the body’s Met requirements (only 50%)
What animals require taurine?
-cats, salmonids,
-likely conditionally essential in dogs too
**not present in plants; must get from animal products
What is taurine needed for?
- Bile acid conjugation
-dogs and cats only use taurine
-rats and humans can use either taurine or glycine - Membrane stabilization
- Modulation of intracellular Ca levels
- Important in high energy cells like heart muscle
What is taurine deficiency linked with?
-Retinal degeneration causing blindness
-impaired reproduction and fetal development
-hearing loss, impaired nervous function
-feline dilated cardiomyopathy
Threonine
Can be deficient in animal diets
-high levels in pulses (legumes), low in grains
Importance of threonine
-High levels of threonine in mucous lining the small intestine and therefore disproportionately high endogenous losses
**even higher losses in mucosal diseases and therefore Threonine requirements are increased
How much threonine is there in mucin?
mucin is made up of 30% threonine
*mucin can not be digested and absorbed so always net loss
Tryptophan
4th limiting amino acid in most diets
-low in corn diets but most diets are fine and have adequate levels of tryptophan
Importance of tryptophan
-can be used to synthesize B-vit niacin
-precursor for serotonin (needed for brain, gut, sleep)
-precursor for melatonin (circadian rhythm control)
Importance of Arginine
Needed in urea cycle to break down amino nitrogen
*carnivores have a high requirement (cats, salmon)
to ensure they can upregulate urea cycle after a meal
Importance of isoleucine, leucine, and valine
- Major components in muscle
- enhance intestinal development, intestinal amino acid transport, mucin production
- Up regulate innate and adaptive immune responses
Is there really an issue of dietary deficiency with isoleucine, leucine, and valine?
No, practical diets have adequate levels
Histidine requirements
Not needed in humans but required in monogastric agricultural species
*rarely deficient in diets
Importance of histidine
Decarboxylation of histidine to histamine
*needed for local immune responses, chemotaxis of WBCs, vasodilation, regulation of gut function
Phenylalanine requirements
-Tyrosine is converted to phenylalanine and can meet part or possibly all of the phenylalanine requirement
*however we assume that tyrosine only meets 50%
Phenylketonuria
A genetic defect in humans that prevent the conversion of tyrosine into phenylalanine
**must avoid aspartame!
Aspartame
-discovered in 1965 by accident
-180x sweeter than sucrose
-metabolized to aspartate, phenylalanine and MeOH in healthy people but in phhenylketonuria can result in neurotoxicity
Glutamine use
-used to synthesize monosodium glutamate (MSG) and glutamate
RESULTS in umami taste receptors
Glutamine requirements in cats
Used in amino acid deamination when amino acids used for energy
*cats have high protein diets so need more
Note: cats can synthesize it but not at an adequate rate
Glycine
Important for nitrogen excretion
-birds/reptiles lay eggs and need to conserve water more than mammals; excrete N as uric acid which contains glycine
Synthetic amino acids
Includes synthetic lysine, methionine, threonine, tryptophan
**because they are often in the shortest supply in plant ingredients
D vs L Amino acids
All amino acids except glycine have both; but L form are natural biologically active isomers
-in synthetic Methionine, D can be converted to L
How are the different synthetic amino acids produced?
Synthetic Lysine, Threonine, Tryptophan= all L= produced by fermentation
Synthetic Met= mix of D and L isomers= produced by industrial process
Hydroxy Analogues of amino acids
-Can buy two kinds of synthetic methionine
1. Methionine
2. Hydroxy-analogue of methionine (MHA)
**MHA can be converted to methionine… but equivalence is not well known
