Regulation of NADH-glutamate dehydrogenase activity by phytochrome, calcium and calmodulin in Zea mays

Abstract

Regulation by the active form of phytochrome (P_FR) and the effect of Ca²⁺ and calmodulin was examined with glutamate dehydrogenase (GDH) of Zea mays. A brief irradiation (5 min) to 5 day old plants with red light resulted in 5-6 fold increase in GDH activity. This effect was nullified when red light was followed immediately by far-red light. The photoreversibility showed that P_FR regulates GDH activity in vivo. To the enzyme extract obtained after EGTA treatment, when Ca²⁺ was added in vitro, GDH was activated by 6 fold. The maximum response by Ca²⁺ was obtained at 80 μM. Both P_AR and Ca²⁺ effects were found to be age dependent. The enzyme activity was inhibited by compound 48/80 in partially purified extracts and the effect was reversed by calmodulin. The purified GDH, however, was not activated directly by calmodulin; it required the presence of another protein factor which was separated by gel permeation column by HPLC. Neither anticalmodulin drugs nor addition of calmodulin had any effect on nitrate re-ductase activity.