Sodium influence on energy transduction by complexes I from Escherichia coli and Paracoccus denitrificans

Abstract

The nature of the ions that are translocated by Escherichia coli and Paracoccus denitrificans complexes I was investigated. We observed that E. coli complex I was capable of proton translocation in the same direction to the established Δ Ψ, showing that in the tested conditions, the coupling ion is the H +. Furthermore, Na + transport to the opposite direction was also observed, and, although Na + was not necessary for the catalytic or proton transport activities, its presence increased the latter. We also observed H + translocation by P. denitrificans complex I, but in this case, H + transport was not influenced by Na + and also Na + transport was not observed. We concluded that E. coli complex I has two energy coupling sites (one Na + independent and the other Na + dependent), as previously observed for Rhodothermus marinus complex I, whereas the coupling mechanism of P. denitrificans enzyme is completely Na + independent. This work thus shows that complex I energy transduction by proton pumping and Na +/H + antiporting is not exclusive of the R. marinus enzyme. Nevertheless, the Na +/H + antiport activity seems not to be a general property of complex I, which may be correlated with the metabolic characteristics of the organisms.