GLYCEROLIPIDS IN VARIOUS PREPARATIONS OF PHOTOSYSTEM-II FROM SPINACH-CHLOROPLASTS

The fatty acid and glycerolipid composition of three types of preparation of Photosystem II (PS II) from spinach thylakoids was studied, namely, the PS II membrane, the PS II core complex, and the PS II reaction center complex. The molecular ratios of lipid to photochemical reaction center II (P680) in these preparations were estimated to be about 150:1, 10:1 and 1:1, respectively. The only lipid molecule found in the PS II reaction center complex was monogalactosyl diacylglycerol (MGDG). This molecule was highly saturated as a result of the presence of hexadecanoic, octadecanoic and tetradecanoic acids; together they accounted for about 50% of the total fatty acids. This composition is in marked contrast to that of MGDG from thylakoid membranes, in which the trienoic fatty acids account for about 90% of the total. The PS II core complex contained MGDG, digalactosyl diacylglycerol and phosphatidylglycerol, but it lacked sulfoquinovosyl diacylglycerol, whereas the PS II membrane contained each of these four glycerolipids. The degree of saturation of the fatty acids in the PS II core complex was intermediate between that in the PS II reaction center complex and that in the PS II membrane. The results are discussed in terms of the structure and function of lipids in the thylakoid membrane. © 1990.