PLANT PHYSIOLOGY , Vol 105, Issue 3 955-964, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Characterization of a Chloroplast Inner Envelope K+ Channel
F. Mi, J. S. Peters and G. A. Berkowitz
Plant Science Department, Cook College, Box 231, Rutgers-The State University of New Jersey, New Brunswick, New Jersey 08903
A K+-conducting protein of the chloroplast inner envelope was characterized
as a K+ channel. Studies of this transport protein in the native membrane
documented its sensitivity to K+ channel blockers. Further studies of
native membranes demonstrated a sensitivity of K+ conductance to divalent
cations such as Mg2+, which modulate ion conduction through interaction
with negative surface charges on the inner-envelope membrane. Purified
chloroplast inner-envelope vesicles were fused into an artificial planar
lipid bilayer to facilitate recording of single-channel K+ currents. These
single-channel K+ currents had a slope conductance of 160 picosiemens.
Antibodies generated against the conserved amino acid sequence that serves
as a selectivity filter in the pore of K+ channels immunoreacted with a
62-kD polypeptide derived from the chloroplast inner envelope. This
polypeptide was fractionated using density gradient centrifugation.
Comigration of this immunoreactive polypeptide and K+ channel activity in
sucrose density gradients further suggested that this polypeptide is the
protein facilitating K+ conductance across the chloroplast inner envelope.
