chapter 30: amino acid degradation and the urea cycle

transamination: alpha-amino acid is transferred to alpha-ketoglutarate to form glutamate with enzyme aminotransferase

first step of amino acid degradation?

oxidative deamination: glutamate releases nitrogen as NH4 by enzyme glutamate dehydrogenase, which regenerates alpha-ketoglutarate

second step of amino acid degradation?

serine, threonine

what are the two amino acids that can be directly deaminated

serine dehydratase and threonine dehydratase

what are the enzymes used to directly deaminate serine and threonine, respectively

leucine, valine, isoleucine

what are the branched chain amino acids that the liver cannot deaminate

pyruvate + NH4 —> alanine which is released into blood. liver takes up alanine and converts it back to pyruvate by transamination. pyruvate can be used for gluconeogenesis and nitrogen enters urea cycle

explain glucose-alanine cycle

NH4 + HCO3 + 2 ATP —> carbamoyl phosphate by carbamoyl phosphate synthetase-1

what is the first step of the urea cycle

carbamoyl phosphate + ornithine —> citralline by ornithine transcarbamoylase

what is the second step of the urea cycle

citralline + aspartate + 1 ATP —> argininosuccinate by argininosuccinate synthetase

what is the third step of the urea cycle

argininosuccinate —> arginine + fumarate by argininosuccinase

what is the fourth step of the urea cycle

arginine + H2O —> urea + ornithine by arginase

what is the fifth step of urea cycle