Isolation and characterisation of a photosystem II reaction centre lipoprotein complex

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Abstract
A photochemically active reaction centre complex has been isolated from photosystem II preparations of spinach chloroplasts by Triton X‐100 solubilisation and sucrose gradient fractionation. Electrophoresis of the complex revealed 5 bands indicating polypeptides of apparent molecular masses of 47, 43, 33, 30 and 10 kDa. Lipid analyses showed that polar, as well as neutral, lipids are associated with the complex. For approx. 40 chlorophyllamolecules there were 3.4 plastoquinone‐9, 3.3 pheophytina, 2.9 β‐carotene, 29.3 monogalactosyldiacylglycerol and 12.4 sulphoquinovosyldiacylglycerol molecules. These results suggest that this photosystem II reaction centre complex, which most likely represents a minimum photochemically active unit, is a lipoprotein complex. A striking feature of the associated polar lipids is their very low degree of unsaturation.