Abstract
Lipids are one of the important constituents of membrane protein complexes, and 14 lipid molecules have been identified in the crystal structure of photosystem II (PSII) from a thermophilic cyanobacterium. In order to study the roles of lipids in PSII, we treated PSII dimer complexes from cyanobacteria and higher plants with phospholipase A2 (PLA2) and lipase. PLA2- and lipase-treatments of PSII from a thermophilic cyanobacterium Thermosynechococcus vulcanus decreased the oxygen-evolving activity by 40% and 16%, respectively. The same treatments of spinach PSII, however, decreased the activities by more than 80% in both cases. Analysis of lipid contents indicated that PLA2- and lipase-treatments decreased the contents of PG and MGDG to a significantly higher degree in spinach PSII than in T. vulcanus PSII. Thus, the association of lipids in spinach PSII is significantly weaker than that in the thermophilic cyanobacterium, which leads to a significantly increased instability of the spinach PSII.
