An enzyme aggregate in the tryptophan pathway of Neurospora crassa.

Abstract

The 1st enzyme in the tryptophan pathway of N. crassa, anthranilate synthetase, is controlled by 2 genetic loci, the tryp-1 and tryp-2 loci. The tryp-1 locus also controls 2 other enzymes in the tryptophan pathway PRA [N-(5[image]-phosphoribosyl) anthranilate] isomerase and InGP [indole-3-glycerolphosphate] synthetase. As a result, mutations at the tryp-1 locus lead to the loss of either anthranilate synthetase or InGP synthetase and PRA isomerase, or, as is usually the case, all 3. On the other hand, mutations at the tryp-2 locus result in the loss of anthranilate synthetase activity only. Anthranilate synthetase, PRA isomerase, and InGP synthetase activities are present in constant ratios over a 90-fold purification range and exhibit identical profiles on zone centrlfugation analysis. These activities are apparently catalyzed by a molecular aggregate which results from the direct interaction of the gene products of the tryp-1 and tryp-2 loci.