The NAD(P)H:peroxide oxidoreductase activity found in crude extracts of hktE- pgdx- H. influenzae Rd cultures has physiologically relevant binding affinities for its reducing substrates NADPH and NADH, while being verylow specific with regard to the oxidizing peroxide substrates H
and t -BOOH. Michaelis-Menten representations of NAD(P)H:peroxide oxidoreductase activity with respect to varying concentrations of (A) reductants and (B) oxidants. Kinetic constants were calculated by fitting the data to the Michaelis-Menten equation using a non-linear curve fit. The amount of total protein used for each kinetic assay was 2.5 mg.