Characterization of three enzymatic forms of glucose-06-phosphate dehydrogenase from Aspergillus oryzae

Abstract

Three forms (I, II and III) of glucose-06-phosphate dehydrogenase were isolated from mycelium of Aspergillus oryzae grown on ribose as the carbon source, by ion-exchange chromatography.The Km values determined for the three forms with respect to glucose-06-phosphate were nearly identical; however the Km for NADP+ were different and the Vmax for the isoenzymatic form II was higher than those for I and III.Inhibition by NADPH was competitive with respect to NADP+, isoenzyme II showing the highest Ki.The optimum pH for forms I, II and III were 9.0, 8.0 and 8.5, respectively, and form I was more thermostable than the others.The apparent molecular weights, determined by gel filtration, were 92,000, 117,500 and 141,000 for forms I, II and III, respectively.