Catabolism of Amino Acids Deamination

Let s now begin a study of some common metabolic pathways by starting with amino acid catabolism. Although the subject is complicated by the fact that each of the 20 a-amino acids in proteins is biologically degraded by its own 

Amino acid catabolism occurs in three stages (1) removal of the a amino group as ammonia, (2) conversion of the ammonia into urea, and (3) conversion of the remaining amino acid carhon skeleton (usually an a-keto acid) into an intermediate that can enter the citric acid cycle. 

Pyruvate, oxaloacetate, a-ketoglutarate, succinyl CoA, fumarate, acetoacetate, or acetyl CoA 

Overall mechanism ofthe enzyme-catalyzed, PLP-dependent transamination of an d-amino acid to give an a-keto acid. Individual steps are explained in the text. 

O An amino acid reacts with the enzyme-bound PLP imine by nucleophilic addition of its -NH2 group to the C=N bond ofthe imine, giving a PLP-amino acid imine and releasing the enzyme amino group. 

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