The involvement of glutamate dehydrogenase and glutamine synthetase/glutamate synthase in ammonia assimilation by the basidiomycete fungus Stropharia semiglobata

Summary: When grown on ammonia as sole nitrogen source, the basidiomycete fungus Stropharia semiglobata assimilated nitrogen via glutamate dehydrogenase (GDH). The two isoenzymes of GDH were both repressed by increasing concentrations of ammonia, but NADP-GDH (EC 1.4.1.4) was far more active than NAD-GDH (EC 1.4.1.2). Glutamine synthetase (GS; EC 6.3.1.2) and glutamate synthase (GOGAT; EC 1.4.7.1) were also active in S. semiglobata and these enzyme activities were independent of the ammonia concentration in the suspension. From enzyme activity and 1 5N-labelling studies of amino acids, it is concluded that both GDH and GS/GOGAT contribute to ammonia assimilation in this fungus.