Glutamate synthase (NADH) from lupin nodules. Specificity of the 2-oxoglutarate site

The binding of substrate analogues including potential alternative substrates, to glutamate synthase (NADH) (L-glutamate: NAD+ oxidoreductase (transaminating) E.C. 1.4.1.14) has been investigated by studying competitive inhibition with respect ot 2-oxoglutarate. Binding requires two terminal carboxyl groups on a C5 straight chain molecule although some C4 molecules bind weakly. Bulky substituents at C2 decrease or prevent binding. Glutarate, the most potent inhibitor, binds much less tightly than the substrate. A 2-oxo group in a molecule other than the substrate does not appear to contribute significantly to binding. None of the analogues was able to act as an alternative substrate.