FEEDBACK INHIBITION OF GLUTAMINE SYNTHETASE OF NEUROSPORA CRASSA BY NICOTINAMIDE-ADENINE DINUCLEOTIDE

Glutamine synthetase of Neurospora crassa is significantly different from that of Escherichia coli. Like the latter, it is subject to feedback inhibition by adenosine monophosphate, glycine, histidine, and cytidine triphosphate, but unlike the E. coli enzyme, it is strongly inhibited by guanosine triphosphate and nicotinamide-adenine dinucleotide. The aromatic amino acids, tryptophan, tyrosine, and phenylalanine, do not inhibit the Neurospora enzyme, but instead, anthranilic acid, the first compound unique to the tryptophan branch of the aromatic amino acid biosynthetic pathway, is an effective inhibitor. Inhibition by nicotinamide-adenine dinucleotide is apparently competitive toward glutamate, noncompetitive toward adenosine triphosphate and uncompetitive with regard to NH2OH. Heat inactivation studies and response to pH show that the catalytic site (glutamate binding) and the regulatory site (nicotinamide-adenine dinucleotide binding) are distinct. © 1968, American Chemical Society. All rights reserved.