Isolation of a Chloroplast N,N′-dicyclohexylcarbodiimide-Binding Proteolipid, Active in Proton Translocation

The N,N′-dicyclohexylcarbodiimide-binding proteolipid from lettuce chloroplast membranes has been purified by a novel, rapid technique involving 1-butanol extraction and ether precipitation. Reconstitution of this proteolipid into liposomes composed of chloroplast lipids and subsequent incorporation of bacteriorhodopsin resulted in the formation of liposomes exhibiting a light-dependent accumulation of protons. This accumulation was significantly enhanced upon addition of N,N′-dicyclohexylcarbodiimide at concentrations similar to those that inhibit chloroplast adenosinetriphosphatase activity. Radioactively labeled N,N′-dicyclohexylcarbodiimide was found to be incorporated essentially into the proteolipid of the reconstituted liposomes. These results suggest that the functional unit responsible for proton channeling in the chloroplast membrane has been isolated and reconstituted in the native state.