Fo part of the ATP synthase from Escherichia coli

Abstract

Four different sets of proteoliposomes were prepared from F₀, subunit c, a complex of subunits a and c (ac complex) and an ac complex supplemented with subunit b. Only liposomes containing intact F₀ or all subunits of F₀ were active in proton translocation and F₁ binding [Schneider, E. and Altendorf, K. (1985) EMBO J. 4, 515–5181. The conformation of subunit c in the different preparations was analyzed by labelling the proteoliposomes with the hydrophobic photoactivatable reagent 3‐(trifluoromethyl)‐3‐(m‐[¹²⁵I]iodophenyl)diazirine ([¹²⁵I]TID). Subsequent isolation and Edman degradation of this polypeptide revealed distinct radioactive labelling patterns over the entire amino acid sequence. In the F₀ complex and in the ac complex subunit c retains a labelling pattern which is related to that found in TID‐labelled membrane vesicles of Escherichia coli [Hoppe et al. (1984) Biochemistry 23, 5610–56161. In the absence of subunit a, considerably more and different amino acid residues of subunit c are modified. The labelling data are discussed in relation to structural aspects of F₀ and functional properties of proteoliposomes reconstituted with F₀ or individual subunits.