Purification and characterization of glucose-6-phosphate dehydrogenase from Aspergillus parasiticus.

Glucose-6-phosphate dehydrogenase (EC 1.1.1.49) was purified from mycelium of Aspergillus parasiticus (1-11-105 Whl). The enzyme had a molecular weight of 1.8 X 10(5) and was composed of four subunits of apparently equal size. The substrate was very strict, only glucose 6-phosphate and glucose being oxidized by NADP or thio-NADP. Zinc ion was a powerful inhibitor of the enzyme, inhibition being competitive with respect to glucose 6-phosphate, with Ki about 2.5 microM. Other divalent metal ions which also serve as inhibitors are nickel, cadmium, and cobalt. It is proposed that the stimulation of polyketide synthesis by zinc ion may be mediated in part by inhibition. of glucose-6-phosphate dehydrogenase.