PLANT PHYSIOLOGY , Vol 108, Issue 4 1725-1734, Copyright © 1995 by American Society of Plant Biologists
Molecular and Physiological Analysis of a Thylakoid K+ Channel Protein
Z. Fang, F. Mi and G. A. Berkowitz
Plant Science Department, Cook College, Box 231, Rutgers-The State University of New Jersey, New Brunswick, New Jersey 08903
Transport studies identified a K+ channel protein in preparations of
purified spinach (Spinacea oleracea) thylakoid membrane. This protein was
solubilized from native membranes and reconstituted into artificial
proteoliposomes with maintenance of functional integrity. A 33-kD thylakoid
polypeptide was identified as a putative component of this thylakoid
protein. This identification was made using an antibody raised against a
synthetic peptide representing a highly conserved region of K+ channel
proteins. K+ channel activity co-migrated with the immunoreactive 33-kD
polypeptide when solubilized thylakoid membrane protein was fractionated on
a Suc density gradient. The antibody was used to immunoprecipitate the
33-kD polypeptide. Physiological function of this thylakoid membrane
protein was elucidated by measuring photosynthetic electron transport of
thylakoid preparations in the presence and absence of a K+ channel blocker.
Results indicated that K+ efflux from the thylakoid lumen through this
channel protein is required for the optimization of photosynthetic
capacity. The effect this protein has on photosynthetic capacity is likely
due to the requirement for K+ efflux from the thylakoid lumen to
charge-balance light-induced proton pumping across this membrane.
