A VOLTAGE-DEPENDENT PORIN-LIKE CHANNEL IN THE INNER ENVELOPE MEMBRANEOF PLANT CHLOROPLASTS

The electrical activity of a single channel of 525 +/- 12 picosiemens in 150 mM KCl was measured after fusion of the inner envelope membrane of the chloroplast with planar lipid bilayers. The reversal potential s measured in KCl gradients indicate that this channel is weakly anion selective (P-Cl/PK = 1.6 +/- 0.2). The gating mechanism of the pore i s voltage dependent. The channel shifts from a fully open state to a s ubstate at positive electrical potentials and remains closed at negati ve electrical potentials, Succinylation of the protein in creases the open probability of the fully open state and reverses the channel sele ctivity. Analysis of the single-channel conductance as a function of t he salt concentration and of the open probability at various voltages suggests that this channel is a new membrane porin not previously iden tified.