Untersuchungen zur Regulation der Ammoniumassimilation von Candida maltosa

Activities of ammonia-metabolizing enzymes from Candida maltosa were measured. The synthesis of glutamate and glutamine involves three primary enzymes: glutamate dehydrogenase (GDH), glutamine synthetase (GS), and glutamate synthase (GOGAT). This yeast has two distinct GDH, the first responsible for glutamate catabolism, and the second solely biosynthetic. The GS is derepressed during growth on low ammonia or on a variety of alternative nitrogen sources, whereas the catabolic GDH (NAD) is repressed under this conditions. Ammonia limitation did not significantly affect GOGAT as well as biosynthetic GDH (NADP) levels. The relatively low K_m-value for ammonia suggest that the GS is catalytically active during cell growth on low concentrations of ammonia. It seems that under N-limitation ammonia assimilation is achieved via GS/GOGAT and under N-excess via GDH/GS.