Schiff base
The mechanism of arginine decarboxylase is analogous to other deaminating and decarboxylating PLP enzymes in its use of a Schiff base intermediate. Initially, Lys386 residue is displaced in a transamination reaction by the L-arginine substate, forming an arginine Schiff base with the PLP cofactor. Decarboxylation of arginine carboxylate group then occurs, where it is hypothesized that the C-C bond broken is perpendicular to the PLP pyridine ring. The pyridine nitrogen group acts as an electron-withdrawing group that facilitates the C-C bond breaking. Protonation of the amino acid leads to the formation of a new Schiff base that subsequently undergoes a transamination reaction by the lysine reside of arginine decarboxylase, regenerating the catalytically active PLP and releasing agmantine as a product. Though it has been hypothesized that a protonated histidine residue involves in the protonation step as a proton source, the identity of the proton-donating residue in arginine decarboxylase has yet to be confirmed.