Wild-type cells of Aspergillus nidulans have undetectable NADL-glutamate dehydrogenase activity when utilizing glucose and high levels of NAD L-glutamate dehydrogenase when utilizing certain amino acids as sole carbon sources.A mutant, designated gdhCl, has appreciable NAD-GDH activity when utilizing glucose as a carbon source. The gdhC1 mutation is semi-dominant and is located in linkage group III.