Nutrition Topic 4
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Nutrition Topic 4
Protein and Amino acid metabolism
What are the 3 classifications of AA?
Indispensable, conditionally indispensable, dispensable
How is metabolic flux of amino acids determined?
By following 'tracers'
What is a nutritionally indispensable AA?
Cannot be synthesized by the animal organism out of materials ordinarily available to the cells at a speed commensurate with the demands for normal growth
Why are amino acids needed?
Plasma AA response
Direct AA oxidation
Indicator AA oxidation
or measure of organ or system function
What are the general aspects of experimental approaches for nitrogen analysis?
All methods should give the same answer
Subjects should be studied at >6 test AA intake levels above and below requirement
Endpoint should show a clear response to change in test AA intake
Question of adaptation to test AA intake
What is indicator AA oxidation (IAAO)?
When an indispensable AA is limiting, then all other indispensable AA wil be oxidized (remember that AA cannot be stored)
Increasing intake of limiting amino acid will decrease IAAO
What is the minimaly invasive IAAO model?
: repeated oral 'nibbling' of tracer solution after 4h feed equilibration
: Breath collection for CO2 enrichment, urine in place of blood for plasma AA enrichment
: D-AA are efficiently excreted in the urine
D- and L- AA can be differentiated by GCMS (gas chromatography mass spectometry) using a 'chiral column'
Why is limiting AA important?
Vegans with lower protein intake and lower protein quality- limiting AA is significant issue especially for children
International- food security and diet diversity- very important especially for children
What is the function of histidine requirement?
Histidine-free diet for 48 days, followed by repletion
No effect on nitrogen balance
Decreased protein turnover, phenelalanine oxidadation
What happens when people are fed 0.6g/kg/d for 7 days?
: protein turnover, albumin synthesis (negative acute phase protein), Glutathione synthesis (antioxidant capacity, increased sysceptibility to oxidative stress)
: Fibrinogen synthesis (positive acute phase protein)
How are amino acids digested?
Pepsin in stomach- acidic pH
Proteases from pancreas in small intestine- luminal digestion
Peptidases on brush border of intestinal epithelial cells
How does the liver play into amino acid metabolism?
: constitutive protein synthesis, plasma protein synthesis, gluconeogenesis, lipogenesis
: amino acid catabolism, urea cycle
Synthesis of dispensible amino acids
High flux rates
High proportion from de novo synthesis
Synthesis accounts for 8% of basal metabolic rate
Ultimate precursor is gucose
Ultimate precursor is glucose (except for tyrosine, for cysteine only the S is from methionine)
What are the issues in sulphur amino acid metabolism?
How does glutathione relate to amino acid synthesis?
Protection agains oxidative stress- conjuction with electrophiles, removeal of ROS
Proteins, lipid membranes, DNA
Immune system function
Does protein have an ergogenic effect?
Probably power but not endurance
Increased lean body mass
: water, osmoregulation
Genes in muscle upregulating myosin, cytoskeleton, protein and glycogen synthesis