Glutamate synthase, an enzyme involved in glutamate biosynthesis in nitrogen-deficient environments, has been purified 200-fold from the photosynthetic bacterium The association of this NADPH-linked glutamate synthase with the photosynthetic membranes was suggested by its co-sedimentation with the chromatophore membranes and its ability to couple glutamate formation to light-generated reducing power. Although it was not homogeneous, the enzyme co-chromatographed with iron after three successive column chromatography steps and had the spectrum of a flavoprotein which suggests it may be an iron-sulphur flavoprotein similar to the enzyme from other prokaryotes. The K values of glutamate synthase for NADPH, glutamine and 2-oxoglutarate were 15 μm, 130 μm and 35 μm, respectively. The molecular weight of glutamate synthase was salt-dependent in that the enzyme isolated in 0.4 m-NaCl showed a molecular weight of 840000, whereas in the absence of salt the molecular weight was about 260000. This phenomenon may be common to other glutamate synthases, since the molecular weight of this enzyme from was also influenced in a similar manner by NaCl.


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