THE ALLOSTERIC NATURE OF NAD-SPECIFIC ISOCITRIC DEHYDROGENASE FROM ASPERGILLI

Abstract

A kinetic study of the NAD-dependent isocitric dehydrogenase from Aspergillus niger (citrate excretor) and A. flavus (nonexcretor) has been made. The enzyme from both sources is markedly and specifically activated by citrate. Analysis of initial velocity data shows that the enzyme possibly has a distinct allosteric site that can bind both isocitrate and citrate, and an active site that is specific for isocitrate. It is conjectured that citrate accumulation by A. niger may be due to a 'desensitization' of the allosteric site of the enzyme by environmental factors.