glucose 6-phosphate dehydrogenase from streptomyces aureofaciens: ligand-induced conformational chang

some kinetic properties of nad+- and nadp+- dependent glucose 6-phosphatedehydrogenase (g6pd) purified from streptomyces aureofaciens were studied. both nadh andnadph inhibited the enzyme competitively and noncompetitively, with respect to the correspondingcoenzymes and glucose 6-phosphate, respectively. atp inhibited the nad+ - linked reaction but not thatof the nadp+- linked activity. the inhibition was competitive with respect to nad+ and noncompetitivewith respect to glucose 6-phosphate. km values were 0.14 mm for nad+ and 0.075 mm for nadp+.similar km values (0.75-0.79 mm) were obtaind for glucose 6-phosphate using either nad+ or nadp+as a coenzyme. the optimum ph was 6.6 for nad+- and 7.4 for nadp+- dependent activity. maximumprotein fluorescence was increased by nad+ (49%) and nadp+ (8%). among bivalent cations studied,cu2+ decreased nad+- linked activity (40%), but increased the nadp+- linked reaction (10%). ni2+ didnot affect nad+- linked, but stimulated nadp+- linked activity. other cations such as zn2+ and mn2+also differently affected the two reactions. the data suggested that binding of nad+ and nadp+produces a different conformational change in s. aureofaciens g6pd or an isomerisation processregulates coenzyme utilization.