Some Properties of the Arginine Decarboxylase in Vicia faba Leaves

Growth of Vicia faba seedlings is accompanied by a rapid increase in arginine decarboxylase (EC 4.1.1.19) in the leaves and epicotyl. Increased enzyme activity was observed under saline conditions in the presence of NaCl and with osmotic stress by mannitol. The partially purified enzyme (about 86-fold) readily decarboxylated L-arginine, while D-arginine, L-homoarginine, L-ornithine and L-lysine were decarboxylated very slowly, and L-citrulline and L-glutamic acid were not decarboxylated. The Km value was 5.8×10−4m for L-arginine. The optimal pH and temperature for activity were 8.5 and 45°C, respectively. p-Chloromercuribenzoate and N-ethylmaleimide were effective inhibitors of the enzyme. Inhibition by spermidine, putrescine and agmatine suggested a possible feed-back mechanism in the pathway of polyamine biosynthesis.