ELECTROPORATION OF THE PHOTOSYNTHETIC MEMBRANE - STRUCTURAL-CHANGES IN PROTEIN AND LIPID-PROTEIN DOMAINS

A biological membrane undergoes a reversible permeability increase through structural changes in the lipid domain when exposed to high external electric fields. The present study shows the occurrence of electric field-induced changes in the conductance of the proton channel of the H+-ATPase as well as electric field-induced structural changes in the lipid-protein domain of photosystem (PS) II in the photosynthetic membrane. The study was carried out by analyzing the electric field-stimulated delayed luminescence (EPL), which originates from charge recombination in the protein complexes of PS I and II of photosynthetic vesicles. We established that a small fraction of the total electric field-induced conductance change was abolished by N,N'-dicyclohexylcarbodiimide (DCCD), an inhibitor of the H+-ATPase, This reversible electric field-induced conductance change has characteristics of a small channel and possesses a lifetime less than or equal to 1 ms. To detect electric field-induced changes in the lipid-protein domains of PS II, we examined the effects of phospholipase A(2) (PLA(2)) on EPL. Higher values of EPL were observed from vesicles that were exposed in the presence of PLA(2) to an electroporating electric field than to a nonelectroporating electric field. The effect of the electroporating field was a long-lived one, lasting for a period greater than or equal to 2 min. This effect was attributed to long-lived electric field-induced structural changes in the lipid-protein domains of PS II.