Purification and properties of glucose-6-phosphate dehydrogenase from Leishmania tropical promastigotes.

Glucose-6-phosphate dehydrogenase specific for NADP (EC 1.1.1.49) was purified to homogeneity from Leishmania tropica promastigotes. The enzyme was found to exist as dimer. The molecular weight of the native enzyme was determined to be 110 000, that of the subunit to be 55 000. The occurence of isoenzymes was demonstrated by isoelectrofocusing. Isoelectric points of glucose-6-phosphate dehydrogenase activity were found at pH 5.5 and pH 6.8. The isoenzymes do not differ with respect to Michaelis constants. The Km-values for NADP and glucose-6-phosphate were determined to be 0.012 mM and 0.15 mM respectively. Glucose-6-phosphate dehydrogenase activity was found to be regulated by product inhibition. The inhibition constant for NADPH was calculated to be 0.05 mM.