The proton-translocating NADH-quinone oxidoreductase in mitochondria (complex I) and bacteria (NDH-1) was shown to be inhibited by amiloride derivatives that are known as specific inhibitors for Na+/H+ exchangers. In bovine submitochondrial particles, the effective concentrations were about the same as those for the Na+/H+ exchangers, whereas in bacterial membranes the inhibitory potencies were lower. These results together with our earlier observation that the amiloride analogues prevent labeling of the ND5 subunit of complex I with a fenpyroximate analogue suggest the involvement of ND5 in H+ (Na+) translocation and no direct involvement of electron carriers in H+ (Na+) translocation.
