Metabolic regulation of the glucose-6-phosphate dehydrogenase from Paracoccus denitrifcans grown on glucose/nitrate.

Glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate : NADP+ L-oxidoreductase EC 1.1.1.49) isolated from Paracoccus denitrificans grown on glucose/nitrate exhibits both NAD+-and NADP+- linked activities. Both activities have a pH optimum of pH 9.6 (Glycine/NaOH buffer) and neither demonstrates a Mg2+ requirement. Kinetics for both NAD(P)+ and glucose-6-phosphate were investigated. Phosphoenolpyruvate inhibits both activities in a competitive manner with respect to glucose-6-phosphate. ATP inhibits the NAD+-linked activity competitively with respect to glucose-6-phosphate but has no effect on the NADP+-linked activity. Neither of the two activities are inhibited by 100 muM NADH but both are inhibited by NADPH. The NAD+-linked activity is far more sensitive to inhibition by NADPH than the NADP+-linked activity.