Part 1.2 Flashcards
Strictly Ketogenic AA
Gluco and ketogenic amino acids
Strictly ketogenic: leu and lys
Glucogenic and ketogenic AA: Ile, Phe, Tyr, Trp, Thr
Everything else is strictly glucogenic
Indispensable amino acids
How Is Lying Like Making Pizza That Tastes Vile
Histidine, Isoleucine, Lysine, Leucine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine
Dispensable amino acids
Alanine, aspartate, asparagine, glutamate and serine
Arginine deficiency
Essential AA for babies and people with illness
Deficiency leads to loss of function in urea cycle leading to increased ammonia which is toxic to the brain
Which amino acid was not previously included in adult requirement recommendations?
Amino acids with the highest intake recommendations (EAR)?
Histidine was thought to only be essential for children
Leucine: 34 mg/kg/day
Lysine: 31 mg/kg/day
Phe/Tyr: 27 mg/kg/day
The optimal amino acid profile does what?
Minimizes catabolism and maximizes protein synthesis
Protein synthesis is only as high as the limiting amino acid content (other AA are catabolized and N balance is negative)
Amino acid deficiencies in specific diets
Inherited diseases related to amino acid metabolism
Pellagra in low tryptophan diets (B3 and/or tryptophan deficiency)
- Trp is a precursor of nicotinamide
Lysine deficiency in corn and soy based diets (agriculture)
Parenteral formulations (some amino acids are not soluble)
AA transporter diseases: Hartnup disease (Trp deficiency) and cystinuria (cysteine stone buildup in kidney and bladder)
Phenylketonuria - lacks enzyme Phe hydroxylase to produce tyrosine
Metabolic response to increasing intake of an essential amino acid like lysine in N balance study
No lysine —> high catabolism (oxidation response) and negative nitrogen balance
Increasing lysine —> decreasing catabolism to approach N balance 0
At lysine requirement —> response (N balance) stays the same but catabolism increases to balance intake
Conditions for test subjects for amino acid studies
Crystalline amino acid diet (tastes terrible)
Collection of all excretion
Due to adaptation period for urea pool requires at least 10 days of diet for each intake level
Requires extreme dedication
How did the inclusion of miscellaneous nitrogen losses affect protein recommendations?
Changes when the requirement line is crossed
.5% of N, leads to an increased requirement of 5-10% per AA
Challenges with the modelling of N balance approach
.5% of N, difficult to calculate when dealing with larger numbers (mg) of amino acids
Curvilinear response as balance approaches zero
Between subject variance
Adaptation of urine pool from multiple trials
Principles of tracer dilution
Approach to measure amino acid flux
Assumptions: system steady state, homogeneity of the pool, massless tracer, no tracer recycling
Flow (Q) = (tracer infusion rate*)/(tracer concentration in pool)
Q = Rate of appearance (I + B) = Rate of disappearance (S + O)
*tracer infusion rate is known so tracer concentration can be measured
How does a tracer amino acid work?
Ex. Leucine containing 1 C13 atom is fed into the diet
Oxidation can be measured from excretion and protein synthesis can be measured from tissue samples
Experiment must be short enough that proteolysis of tracer doesn’t occur
Stable isotope tracers
Isotopomers
C13, H2 (deuterium), N15, O18, S34
1-13^C Leucine
5,5,5-2^H3 Leucine
How does a gas chromatograph mass spectrometer work?
1) Sample is heated, pumped into extremely low air pressure (vacuum)
2) Molecules bombarded by high energy electrons which explodes molecules into patterns of fragments
3) Passes through lenses, and through quadrupole where ions spiral out and are analyzed
