Arginine and Ornithine Decarboxylases, the Polyamine Biosynthetic Enzymes of Mung Bean Seedlings

Abstract

General properties and relative activities of L-arginine decarboxylase (ADC) (EC 4.1.1.19) and L-ornithine decarboxylase (ODC) (EC 4.1.1.17), 2 important enzymes in putrescine and polyamine biosynthesis, were investigated in mung bean (V. radiata L.) tissues. Both activities increase linearly with increasing concentrations of crude enzyme, but the increase in ADC activity is considerably greater. The decarboxylation reaction is linear for up to 30-60 min and both enzymes have a pH optimum of 7.2. .alpha.-Difluoromethyl-ornithine inhibits ODC activity of excised roots, while increasing ADC activity. High specific activity of both enzymes occurs in terminal buds and leaves, while root and hypocotyl activity are low. Different ADC-to-ODC activity ratios occur in various tissues of mung bean plants. Substantial increase in the activity of both enzymes is detected in incubated sections as compared with intact plants. A comparison of several plant species [Phaseolus vulgaris and Gossypium hirsutum]indicates a wide range of ADC-to-ODC activity ratio. Evidently, ADC and ODC are active in plant tissues and their relative contribution to putrescine biosynthesis is dependent upon the type of tissue and growth process.