catabolism of amino acids Flashcards
what stimulates the synthesis of N-acetylglutamate?
arginine
why will hyperammonemia cause CNS defects?
high NH4 leads to depletion of TCA cycle intermediates as well as decreased synthesis of NTs (all of the intermediates are busy trying to excrete the excess NH4)
what occurs with ornithine transcarbamoylase deficiency?
enzyme responsible for carbamoyl phosphate + ornithine –> citrulline is deficient, leads to high NH4/glutamine in the blood, “orotic acuduria” is the defining feature
how does orotic acuduria occur?
in OTC def, levels of carbamoyl phosphate increase and spill out of the mitochondria into the cytosol. CPS II (present in cytosol) converts it to orotic acid, which accumulates and can be found in the urine
what is an essential aa if OTC deficiency is present?
arginine. Since it is usually synthesized during the urea cycle, but cannot be synthesized if urea cycle cannot run
causes of elevated BUN? increased urinary NH4+ excretion?
inc BUN = impaired renal function/dehydration
inc NH4 = acidosis, starvation
glucogenic aa (3)
alanine, aspartate, glutamate
ketogenic aa (2)
leucine, lysine
both ketogenic and glycogenic aa
isoleucine, phenylalanine, tryptophan, tyrosine, threonine
tryptophan catabolism results in the production of-
Niacin
what is affected in maple syrup urine disease?
catabolism of branched chain aa because of defect in a-keto acid decarboxylase. ketoacidosis will occur because first step (transamination) occurs as usual
some pts with MSUD will respond to therapy with __ because?
thiamine
a-ketoacid dehydogenase complex has multiple subunits. E1 catalyzes a decarboxylation that uses thiamine as a cofactor.
PKU typically results from a defect in
phenylalanine hydroxylase
what becomes an essential aa when PKU present?
tyrosine
what cofactor is used by Phe hydroxylase
BH4 (tetrahydrobiopterin)
