Amino Acid Metabolism and Urea Cycle Flashcards
What coenzyme do transaminases require and what vitamin is it derived from?
PLP from B6
What are the ketogenic amino acids?
Leu, Lys
What are the keto/glucogenic amino acids?
Phe, Ile, Trp, Tyr, Thr
What is homocystinuria?
Build up of homocysteine due to defect in Cystathionine ß-Synthase.
Inability to fully convert Met to end product
How does B6 contribute to homocystinuria?
Cystathionine ß-Synthase needs PLP to function. PLP needs B6 to function so overall cause is a deficiency in B6
What leads to Maple Syrup Urine disease?
Defect in BC alpha-keto acid dehydrogenase and its ability to convert BCAAs to succinyl-CoA
What leads to PKU?
Defect in phenylalanine hydroxylase to convert Phe –> Tyr.
Primary = deficiency in phenylalanine hydroxylase
Secondary = deficiency in THB (needed for conversion)
Explain glutamate dehydrogenase…
Alpha-KG + NH4 –> Glu (in brain)
Explain glutamine synthase…
Glu + NH4 –> Gln (in brain)
Explain glutaminase…
Gln –> Glu + NH4 (in liver)
Explain ALT…
Pyruvate + Glu –> Ala (in muscle)
Then…
Ala –> Pyruvate + Glu (in liver)
*Glutamate dehydrogenase then converts Glu –> alpha-KG, releasing NH4 to enter urea cycle
Explain carbamoyl phosphate synthetase…
NH4 –> carbamoyl phosphate (urea cycle)
*Rate limiting step
What Dx is associated with a defect in carbamoyl phosphate synthetase?
Hyperammonemia
Explain ornithine transcarbamoylase…
Carbamoyl phosphate + ornithine –> citrulline (urea cycle)
What Dx is associated with a defect in ornithine transcarbamoylase?
Hyperammonemia w/ orotic aciduria
