Characterization of extracellular menadion-catalyzed H2O2 production by NIH/3T3 cells.

The extracellular menadione-catalyzed H2O2 production by NIH/3T3 cells was expected to depend on plasma membrane-bound NAD(P)H:quinone oxidoreductase. This enzyme was estimated to be a flavoprotein with the molecular mass of 70 KDa. Km values of plasma membrane-bound NAD(P)H:quinone oxidoreductase producing H2O2 were 60 microM for NADH and 150 microM for NADPH. Ca2+ ionophore A23187 controlled menadione-catalyzed H2O2 production by the cells in time- and concentration-dependent manner.