K-CONDUCTING ION-CHANNEL OF THE CHLOROPLAST INNER ENVELOPE - FUNCTIONAL RECONSTITUTION INTO LIPOSOMES()

Potassium flux between the chloroplast stroma and cytoplasm is known t o be indirectly linked to H+ countertransport and, hence, stromal pH a nd photosynthetic capacity. The specific molecular mechanism that faci litates K+ flux across the chloroplast envelope is not known and has b een a source of controversy for well over a decade. The objective of t his study was to elucidate the nature of this envelope protein. To thi s end, solubilized protein in detergent extracts of purified chloropla st inner envelope vesicles was reconstituted into artificial liposomes , and cation fluxes into these proteoliposomes were measured. Results of inhibitor studies and counterflux experiments indicated that a K+-c onducting ion channel was solubilized and functionally reconstituted i nto the proteoliposomes. This transport protein may be a nonspecific m onovalent cation channel. This report represents a direct demonstratio n of ion channel activity associated with the limiting (inner) membran e of the chloroplast envelope.