Respiratory complex I from Escherichia coli does not transport Na+ in the absence of its NuoL subunit

We investigated H⁺ and Na⁺ transport by complex I from Escherichia coli devoid of the NuoL subunit, which is probably part of the ion translocating machinery. We observed that complex I devoid of the NuoL subunit still translocates H⁺, although to a smaller extension than the complete version of complex I, but does not transport Na⁺. Our results unequivocally reinforce the observation that E. coli complex I transports Na⁺ in the opposite direction to that of the H⁺ and show that NuoL subunit is involved in the translocation of both ions by complex I.