Extraction and stability of the pigment-protein complexes of the photosystem 2 from membranes of the unicellular alga Dunaliella salina: effect of glycerol.

Effects of glycerol on the extraction efficiency and the stability of pigment-protein complexes (PPC) of photosystem 2 (PS2) from membranes of the green unicellular alga Dunaliella salina were studied. PS2 membranes were extracted with the detergent n-dodecyl-beta-maltoside (DM) in the presence of 4 M glycerol and 1 M NaCl at a DM:chlorophyll ratio of 15:1 (w/w). The extracts were purified on a DEAE fractogel 650S column. To assess the effect of glycerol on the PPC stability, PS2 membranes were illuminated with white light of high intensity. Then PPCs were extracted and studied spectroscopically and using PAG electrophoresis under denaturing and native conditions. It was found that addition of 4 M glycerol and 1 M NaCl to the extraction medium affects the extraction of the PS2 PPCs but not of the light-harvesting chlorophyll a/b protein (LH2). It was shown that 4 M glycerol protects PS2 from the destructive effects of intense white light, high NaCl concentration, and the detergent Triton X-100. It is suggested that, apart from its osmotic action, glycerol performs a protective function and stabilizes PS2 PPCs in the cells of Dunaliella salina.