Roles of lipids in photosystem II from cyanobacteria

Abstract

In order to study the roles of lipids in PSII from Thermosynechococcus vulcanus, we used phospholipase A₂ (PLA₂) and lipase to treat PSII core complex and examined their effects on PSII structure and functions. The following results were obtained: 1. PLA₂-treatement decreased the content of PG by 70.6%, leading to a decrease of 40% in oxygen evolution. In contrast, lipase-treatment specifically decreased the content of monogalactosyldiacylglycerol (MGDG) by 71.2% without affecting the contents of other lipids, resulting in a decrease of 16% in oxygen evolution. These indicated that PG was more important than MGDG in maintaining the PSII function. 2. PLA₂-treatment induced neither the dissociation of PSII dimer nor any loss of polypeptides from the PSII core complex. 3. Depletion of PG did not affect the water oxidation site, but caused a damage to the Q_B binding site, leading to an inhibition in the electron transfer from Q_A to Q_B.