This view shows introducing 11 pairs of cysteine mutations into Complex I; in each pair one is in the lateral helix, and the other is in a nearby region of subunit N, M, or L.; Short distance cross-links, which were formed by disulfide bonds, are colored red, whereas longer distance cross-links formed by bifunctional methane thiosulfonates are colored green. The activity of Complex I decrease by>10–20%;as indicated by deamino-NADH oxidase activity or rates of proton translocation. (Subunit L is colored blue, subunit Mis magenta, subunit N is green, and subunits A, J, and K are colored gray.)

   In contrast, two pairs of cysteine mutations introduced at other interfaces of N:M.Cross-linking:M145C (M) -M388C (N) and A155C (M) - V430C (N);activity of 145–388 dropped by 30% and that of 155–430 dropped by 50%, and in both cases, the proton translocation activity almost totally lost.

  19 mutations in each of two positions of subunit L,M,N- L_K169, M_K173, N_K158(color pink) and L_Q236, M_H241, N_H224(color cyan);Corresponding mutations in the three subunits were found to have very similar effects on all activities measured;The results provide evidence that the L, M, and N subunits have a common role in Complex I.

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