Sulfolipid associated with the light-harvesting complex associated with photosystem II apoproteins of Chlamydomonas reinhardii

Abstract

In the light-harvesting chlorophyll a/b- protein complex (LHC II) of the green alga Chlamydomonas reinhardii three immunologically cross-reacting LHC II-apoproteins of about 24, 25 and 29 kDa can be distinguished by SDS gel electrophoresis. When digested with S. aureus V8 protease, their proteolytic fragmentation patterns are characteristically different. The very hydrophobic apoproteins have been isolated on a preparative scale by extraction of crude thylakoids with organic solvents and subsequent purification by gel chromatography. Further analysis of the purified, colourless apoproteins by transesterification with sodium methoxide and gas liquid chromatography showed that per 1 mol of protein, they contain about 4 mol of fatty acids, 80% of them being palmitic acid. Separation by TLC revealed that the presence of palmitic acid in the LHC II-apoproteins is not due to covalent binding, but to a specific association of these proteins with sulfoquinovosyldiglycerol (SQDG). Sulfoquinovose was also identified by HPLC of the dansylhydrazine derivative. Also LHC II-apoproteins were isolated from the chlorophyll b- deficient mutant pg-113, from which no LHC II-complex can be prepared. The tightly bound lipids of the mutant apoproteins had almost the same composition as those of the wild type.