A new assay for ferredoxin-dependent glutamine oxoglutarate amino transferase (glutamate synthase) using electrolytically reduced methyl viologen

A new, quick assay is described for ferredoxin-dependent glutamate synthase from leaves, using electrolytically reduced methyl viologen. Activity, which is stimulated fivefold by ferredoxin, is measured spectrophotometrically as oxidation of methyl viologen. The assay does not require routine estimation of glutamate. Two molecules of glutamate were shown to be formed during the oxidation of two molecules of methyl viologen. Activities correspond to those previously reported for leaf homogenates. © 1980.