The enzyme uses pyridoxal phosphate (PLP), the active form of vitamin B6, as a cofactor. PLP is essential to the mechanism of decarboxylation in<unk> . In the active enzyme, PLP is bound to lysine-303 of<unk>  as a Schiff base. Upon substrate binding, Lys-303 is displaced by the substrate's<unk> . This positions the carboxylate of the substrate within the active site such that decarboxylation is favored. Decarboxylation of the substrate produces a quinonoid intermediate, which is subsequently protonated to produce a Schiff base adduct of PLP and the<unk> d product. Lys-303 can then regenerate the original Schiff base, releasing the product while retaining PLP. Probing this PLP-catalyzed decarboxylation, it has been discovered that there is a difference in concentration and pH dependence between substrates. DOPA is optimally<unk> d at pH 5.7 and a PLP concentration of 0.125 mM, while the conditions for optimal 5-HTP decarboxylation were found to be pH 8.3 and 0.3 mM PLP. Mechanism of<unk>
Aromatic L-amino acid decarboxylase
Phenylalanine hydroxylase
Monoamine oxidase B
Catechol-O-methyltransferase
Tyrosine hydroxylase
Dopamine beta-hydroxylase
Monoamine oxidase A
Monoamine oxidase