Separation of two forms of glutamate synthase in leaves of tomato (Lycopersicon esculentum).

Two forms of glutamate synthase, one dependent on NAD(P)H, and the other on ferredoxin, have been completely separated by ionic exchange chromatography on DEAE cellulose. The NAD(P)H dependent enzyme was further purified by affinity chromatography with Blue Sepharose, showing Km values of 0.5 mM, 0.3 mM and 1.7 microM for glutamine, 2-oxoglutarate and NADH, respectively. Ferredoxin dependent enzyme was also purified to electrophoretic homogeneity; the Km values were 0.5 mM, 0.2 mM and 0.2 microM for glutamine, 2-oxoglutarate and ferredoxin, respectively. These results support the glutamine synthetase - glutamate synthase pathway for nitrogen assimilation.