evidence for the essential arginine and histidine residues in catalytic activity of glucose 6-phosphate dehydrogenase from streptomyces aureofaciens

glucose 6-phosphate dehydrogenase (g6pd) was purified from streptomyces aureofaciens and inactivated with butanedione and diethylpyrocarbonate. incubation of the enzyme with butanedione resulted in a rapid activity loss (80%) within 5 min, followed by a slow phase using a molar ratio to enzyme concentration of 100. fluorescence studies showed a conformational change in the butanedione-modified enzyme. nad+, nadp+ and glucose 6-phosphate protected the enzyme against inactivation. diethylpyrocarbonate (2 mm) completely inactivated the enzyme after 2 min. stoichiometry of the inactivation showed 2 moles of histidine residues per mole of enzyme with complete activity loss. maximum emission spectrum of the enzyme decreased (23%) upon modification and the presence of nad+ or nadp+ further decreased the fluorescence by 27% and 10.5%, respectively. the data suggest that essential arginine and histidine residues may be involved in the catalytic activity of streptomyces aureofaciens g6pd