PHOSPHATIDYLGLYCEROL AND BETA-CAROTENE BOUND ONTO THE D1-CORE PEPTIDEOF PHOTOSYSTEM-II IN THE FILAMENTOUS CYANOBACTERIUM OSCILLATORIA-CHALYBEA

Photosystem II-particles from the cyanobacterium Oscillatoria chalybea were isolated by fractionating centrifugation. Purification of these particles was achieved by a 22 hours centrifugation over a linear sucr ose density gradient at 217.500 X g. The obtained particle fraction ex hibited an oxygen evolution activity which corresponded to three times the rate of intact cells and to five times the rate of intact thylako ids. The chlorophyll protein ratio was 1:10 and the ratio manganese/ch lorophyll 1:34. SDS-polyacrylamide gel electrophoresis showed that the photosystem II-fraction is composed of the core peptides D 1 and D 2, the chlorophyll-binding peptides CP 43 and CP 47, the extrinsic 33 kD a peptide (manganese stabilizing peptide, MSP) and phycobiliproteins w ith molecular masses between 16 to 20 kDa. Cyt b(559) was not detected in our gel electrophoresis assay. Part of the peptides of the 30 kDa- region (D 1, D 2, MSP) occurred as aggregates with a molecular mass of 60 to 66 kDa. The D 1-peptide was isolated from the PS II-preparation by SDS-gel electrophoresis. The intrinisic peptide reacts in the West ern blot procedure with the antiserum to phosphatidylglycerol and with the antiserum to beta-carotene. Incubation of the peptide with the an tisera to monogalactosyldiglyceride, sulfoquinovosyldiglyceride and ze axanthine resulted negatively. The binding of phosphatidylglycerol ont o the D 1-peptide was confirmed by lipid analysis in HPLC and fatty ac id analysis by gas chromatography. Only this Lipid, respectively the t ypical fatty acid mixture of this lipid was detected. The lipid is cha racterized by the fact that the hexadecenoic acid does not exhibit tra ns-configuration, as is true for phosphatidylglycerol of higher plants and algae, but occurs in cis-configuration. With the antibody being d irected towards the glycerol-phosphate residue and not towards the fat ty acids, it can be concluded from the reaction of the antibodies with the bound lipid that the Lipid is bound to the peptide via the fatty acid. The negatively charged phosphatidylglycerol increases the hydrop hobicity of the peptide and leads to a negatively charged surface favo uring binding of cations like calcium and magnesium. The fact that inc ubation of this PS II-fraction with phospholipase inhibits photosynthe tic activity by 25% which can be fully restored by addition of phospha tidylglycerol, shows that bound phosphatidylglycerol has a functional role.