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

A biological membrane undergoes a reversible permeability increase thr ough structural changes in the lipid domain when exposed to high exter nal electric fields. The present study shows the occurrence of electri c field-induced changes in the conductance of the proton channel of th e H+-ATPase as well as electric field-induced structural changes in th e lipid-protein domain of photosystem (PS) II in the photosynthetic me mbrane. The study was carried out by analyzing the electric field-stim ulated delayed luminescence (EPL), which originates from charge recomb ination in the protein complexes of PS I and II of photosynthetic vesi cles. We established that a small fraction of the total electric field -induced conductance change was abolished by N,N'-dicyclohexylcarbodii mide (DCCD), an inhibitor of the H+-ATPase, This reversible electric f ield-induced conductance change has characteristics of a small channel and possesses a lifetime less than or equal to 1 ms. To detect electr ic field-induced changes in the lipid-protein domains of PS II, we exa mined 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 nonelectropor ating electric field. The effect of the electroporating field was a lo ng-lived one, lasting for a period greater than or equal to 2 min. Thi s effect was attributed to long-lived electric field-induced structura l changes in the lipid-protein domains of PS II.