FIGURE 3.

Cross-linking between the HL helix and subunit M using Cu²⁺ ions. A, representative immunoblots of membrane samples from the wild type strain and from two mutants, A557C (nuoL) + A307C (nuoM) and L565C (nuoL) + P239C (nuoM), are shown with and without treatment with Cu²⁺ ions to promote disulfide formation. The antibody used was against subunit M. B, the effect of Cu²⁺ treatment on the deamino-NADH oxidase activity of the wild type strain and the same two mutants is shown. Results are the means and S.E. of at least four measurements from at least two membrane preparations. C, proton translocation assays of the wild type and the same two mutants with and without treatment with Cu²⁺ ions. The fluorescence quenching of ACMA was initiated by deamino-NADH and was reversed by the addition of FCCP.