BIOC 311 Lecture Notes - Lecture 30: Ornithine, Threonine, Benzoic Acid
18 Jun 2016
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Goal: get rid off amino group produced by aa catabolism. Require atp for production of first substrate (synthesis of carbomoyl phosphate) by cps-1 (regulated by nag, synthesis of nag is regulated by nags and is stimulated by arginine) First step occurs in mitochondria, while the others steps occur in cytosol of liver cells. Urea is secreted in urine from kidneys (2% urea). Note that there is no significant amount of aa in urine, and if find some you have a problem. If you follow the nitrogen, one is from oxidative deamination of glutamate by gdh (upstream of urea cycle) and the second is from aspartate. In the matrix of mitochondria, aspartate transaminase catalyses reaction where amino group of glutamate is transferred onto oa forming aspartate. Localization of enzymes and concentration of substrates in location dictates direction of reaction. For instance, there is a cytosolic aspartate transaminase that performs the reverse reaction in cytosol.
