The action of tributyltin chloride on energy-dependent transhydrogenation of NADP+ by NADH in membranes of Escherichia coli

Abstract

Respiration- and ATP-dependent transhydrogenation of NADP+ by NADH in everted membrane vesicles from Escherichia coli is inhibited by nigericin but is relatively insensitive to valinomycin. The sensitivity to nigericin is enhanced 30-fold in the presence of valinomycin. It is concluded that both the transmembrane pH difference and the membrane potential constitute the driving force for energy-dependent transhydrogenation.Respiration- and ATP-dependent transhydrogenation are inhibited by tributyltin chloride. Although effects on the energization system have not been excluded, the inhibitor appears to react with a sulfhydryl group on the transhydrogenase enzyme. This inhibition is not dependent on the presence of a permeant anion and can be reversed by mono- and particularly di-thiol compounds. The transhydrogenase is also inhibited by 5,5′-dithiobis(2-nitrobenzoic acid), N-ethylmaleimide, p-chloromercuriphenyl sulfonic acid, and Zn2+, but these reagents are less effective than tributyltin chloride. Energy-independent transhydrogenation is inhibited at high concentrations (20 mM) of cysteine. The reason for this is unknown.