Quantitative immunochemical evidence for identical topography of subunits CF₀II and CF₀I within the photosynthetic ATP‐synthase of spinach chloroplasts

Monospecific polyclonal antisera against the 16 kDa and the 18 kDa polypeptides II and I from the CF 0 moiety of the photosynthetic ATP‐synthase in spinach were produced. Inhibition, agglutination and absorption experiments were combined with quantitative determinations in ELISA of residual antibodies and of amounts of CF 0 and CF 1 . It follows that subunits CF 0 II and CF 0 I are membrane anchored, extend into the matrix space, and are partially shielded underneath or within CF 1 . These results on the structure suggest that CF 0 II and CF 0 I are homologous to each other, and in function both homologous to E. coli F 0 b; thus CF 0 II together with CF 0 I would be part of the ‘stalk’.