Cation channels by subunit III of the channel portion of the chloroplast H⁺‐ATPase

The chloroplast H + ‐ATPase (CF 0 CF 1 ) was isolated and reconstituted into lipid vesicles by dialysis technique. Vesicles were fused by dehydration/ rehydration to obtain cell‐size liposomes, which were studied by patch‐clamp techniques. Single‐channel activity was observed with several conductance levels in the range of some 10 pS (100 mM KCl). In contrast to intact CF 0 , which conducts protons, only (even at pH 8), these channels were permeable for potassium and sodium. Venturicidin, which blocks proton flow through intact CF 0 , here greatly decreased the single‐channel open probability. Subunit III of CF 0 , alone, yielded cation channels resembling the former. Our tentative interpretation is, that dearrangement or fragmentation of CF 0 caused the potassium and sodium permeability, which, however, is suppressed in intact CF 0 .