Scheme of the net reaction catalyzed by alanine transaminase (glutamic acid-pyruvic acid transaminase, GPT).
In the first half-reaction (1) L-alanine is converted to pyruvate with the concomitant conversion of the Lys-PLP Schiff-base linked cofactor to free Lys and PMP (in AlaA, the catalytic lysine residue is Lys240). In the second and last half-reaction (2), a molecule of 2-oxoglutarate is converted to L-glutamate and PMP is recycled back to the enzyme’s resting state cofactor (Lys240-PLP). In the net reaction scheme, a lonely electron pair is shown beside the reactive amine groups of L-alanine and L-glutamate. In the case of valine-pyruvate transaminase (AvtA), the incoming oxo acid is 3-methyl-2-oxobutanoate yielding L-valine as the corresponding α-amino acid instead of L-glutamate.