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‘Glutamine(amide): 2-Oxoglutarate Amino Transferase Oxido-reductase (NADP)’, an Enzyme Involved in the Synthesis of Glutamate by Some Bacteria
Abstract
SUMMARY: Ammonia-limited Aerobacter aerogenes, Erwinia carotovora, Pseudomonas fluorescens, Bacillus subtilis and B. megaterium synthesized glutamate from NH3 and 2-oxoglutarate by a process that involved first the synthesis of glutamine and then the reductive transfer of the glutamine amide-nitrogen to the 2-position of 2-oxoglutarate. The latter step required the recently reported enzyme ‘glutamine(amide): 2-oxoglutarate amino-transferase oxido-reductase (NADP)', some further properties of which are described here. This enzyme, from different organisms, always had a well-defined maximum activity at a pH value between 7·5 and 8·0; it had an apparent Km for 2-oxoglutarate between 0·1 and 2·0 mm and an apparent Km for glutamine between 0·2 and 1·8 mm. Glutamate (the metabolic end-product) and Mg2+ strongly inhibited the enzyme from Gram-negative bacteria but less so that from Gram-positive species. Synthesis of glutamate by this enzyme required NADPH, and NADH was inactive; pyruvate, oxaloacetate, 2-oxobutyrate and 2-oxoisovalerate could not substitute for 2-oxoglutarate, nor could the requirement for glutamine be met by asparagine, citrulline, arginine or urea. Although conditions that favoured the synthesis of this enzyme generally also favoured synthesis of glutamine synthetase and caused suppression of glutamate dehydrogenase formation, a close correlation between the bacterial contents of these different enzymes was not apparent.
- Accepted:
- Published Online:
© Society for General Microbiology 1970