Neighbouring subunits of CF₀ and between CF₁ and CF₀ of the soluble chloroplast ATP synthase (CF₁‐CF₀) as revealed by chemical protein cross‐linking

Neighbouring subunits of CF 0 (I–III) and between cf 0 and CF 1 (α‐ϵ) of the chloroplast ATP synthase have been examined by cross‐linking with Cu‐phenanthroline (CuP) and bifunctional, cleavable imidoesters. Imidoesters caused cross‐links of α‐II, β‐I, β‐II, γ‐II, δ‐I and ϵ‐III as well as of I 2 , I–III, II–III and III 2 of the CF 0 portion. subunits α‐II, β‐I, β‐II, γ‐II and I‐I are close enough to form intermolecular cystine bridges upon CuP‐catalyzed oxidation of sH groups. The results indicate that: (i) mainly interactions of the CF 1 subunits α, β and γ with the CF 0 polypeptides I and II are required for binding of CF 1 to the thylakoid membrane; (ii) subunit ϵ interacts directly with CF 0 ‐III; (iii) the CF 0 portion contains a dimer of subunit I; (iv) subunits α and β appear to be structurally non‐equivalent within the protein complex.