The activity of NADH-, NADPH- and Fd-dependent glutamate synthase in the plastids and cytosol of Pisum arvense L. root cells

Abstract

Three forms of glutamate synthase (NADH-GOGAT, NADPH-GOGAT and Fd-(ferredoxin) GOGAT) were found in the plastids and cytosol of Pisum arvense root cells. The activities of the enzymes of both fractions decreased with increasing age of the plants, with the exception of plastid NADPH-GOGAT which exhibited markedly stable activity. NADH-GOGAT dominated in the cytosol of root cells of several day-old plants but after 14 days of cultivation, the activities of all of the GOGAT forms equalized. Plastid NADH-GOGAT and Fd-GOGAT showed similar activities in the root cells of 3-5 day-old plants, with Fd-GOGAT becoming the dominant enzyme form after 14 days. The entire activity of NADH-GOGAT and Fd-GOGAT was confined to the plaslid stroma. The plastid membrane fraction contained 37% of the NADPH-GOGAT activity. Isolated plastids synthesized glutamate from 2-ketoglutarate and glutamine, and glucose-6-phosphate and 6-phosophogluconate clearly stimulated this process. It is supposed that the synthesis of glutamate in Pisum arvense root plastids may be dependent on the intensity of the carbohydrates conversion in the pentose phosphate pathway.