DIRECT EVIDENCE FOR THE PRESENCE OF 2 EXTERNAL NAD(P)H DEHYDROGENASESCOUPLED TO THE ELECTRON-TRANSPORT CHAIN IN PLANT-MITOCHONDRIA

Exogenous NADPH oxidation by purified mitochondria from both potato tu ber and Arum maculatum spadix was completely and irreversibly inhibite d by sub-micromolar diphenyleneiodonium (DPI), while exogenous NADH ox idation was inhibited to only a small degree. Addition of DPI caused t he collapse of the membrane potential generated by NADPH oxidation, wh ile the potential generated by NADH was unaffected, We conclude that t here are two distinct enzymes on the outer surface of the inner membra ne of plant mitochondria, one specific for NADH, the other relatively specific for NADPH, with both enzymes linked to the electron transport chain.