Activities and properties of the ammonium assimilation enzymes NADP-dependent glutamate dehydrogenase (GDH), glutamate synthase (GOGAT) and glutamine synthetase (GS) were determined in batch and continuous cultures of . NADP-dependent GDH activity showed allosteric kinetics, with an S for 2-oxoglutarate of 7·5 mM and an apparent for ammonium of 5·0 μ. GOGAT activity was affected by the buffer used for extraction and assay, but in phosphate buffer, kinetics were hyperbolic, yielding values for glutamine of 750 μM and for 2-oxoglutarate of 65 μm. The enzymes GOGAT and NADP-dependent GDH were also assayed in batch cultures of and three other pathogenic spp.: and . Evidence is presented that GS/GOGAT is a major pathway for ammonium assimilation in and that this pathway is also significant in other species.


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