Characterization of a chloroplast inner envelope K+ channel.
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.
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Plant Science Department, Cook College, Rutgers-State University of New Jersey, New Brunswick 08903.
Peters
J S
JS
Berkowitz
G A
GA
D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000502:physiology*; D017124:Conserved Sequence; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D007425:Intracellular Membranes / Q000502:physiology*; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D008970:Molecular Weight; D015221:Potassium Channels / Q000737:chemistry / Q000302:isolation & purification / Q000502:physiology*; D014675:Vegetables / Q000502:physiology*
D015221:Potassium Channels