Effects of D-glutamate on mycelial growth and glutamate dehydrogenase enzymes of Coprinus lagopus.

D-Glutamate inhibited hyphal extension, the degree of inhibition depending on the identity of the glutamate dehydrogenase (GDH) enzyme present in the mycelium. Mycelia were most sensitive to inhibition on media which promoted formation of the NAD-linked GDH. The activity of this enzyme was inhibited by D-glutamate in experiments with cell-free extracts, the inhibitions being noncompetitive or mixed. Similarly the activity of the NADP-linked enzyme (GDHNADp) was inhibited in its utilization of ammonium ions (in the amination reaction) and L-glutamate (in the deamination reaction). In contrast, 2-oxoglutarate was a co-operative substrate for GDHNADp in the amination reaction and Dglutamate acted as an allosteric activator. D-Glutamate was also able to derepress the synthesis of GDHNADp; the NAD-linked enzyme was hardly affected.