Nitrogen regulation in microorganisms

The central role of NH sub(4) super(+)-assimilation in the microbial metabolization of several anorganic nitrogen sources and the regulation of its key enzymes - glutamate dehydrogenases (GDH-EC 1.4.1.2. and EC 1.4.1.4.), glutamine synthetase (GS-EC 6.3.1.2.) and glutamate synthase (GOGAT-EC 1.4.1.3.) - are presented. In excess of ammonia gram-negative bacteria as well as yeasts assimilate this ion in a NADH + H super(+) or NADPH + H super(+) dependent reaction by GDH. Under NH sub(4) super(+)-limitation - in natural environments rather the rule than the exception - the ammonia assimilation is ATP dependent and catalyzed via GS and GOGAT. Subsequently the connection between the nitrogen metabolization and the resulting changes in the extracellular pH of growing yeast cultures is discussed.