Arginine decarboxylase of oats is activated by enzymatic cleavage into two polypeptides

Oat arginine decarboxylase is synthesized as a 66-kDa proenzyme, but the soluble enzyme is found in oats as a complex of 42- and 24-kDa polypeptide fragments, both derived from the 66-kDa precursor. We report here that this proteolytic cleavage is the result of a processing enzyme, distinct from arginine decarboxylase itself, that leads to activation of the arginine decarboxylase. The proteolysis is resistant to a standard set of protease inhibitors, but is inhibited by high concentrations of Zn2+, as is the activation of arginine decarboxylase. Agmatine, putrescine, spermidine, and spermine, as well as the arginine decarboxylase inhibitor difluoromethylarginine, each had no effect on the reaction. Oat arginine decarboxylase is thus similar to some other amino acid decarboxylases in requiring a proteolytic cleavage for activation; however, it differs in that the other examples are auto-catalytic self-processing.