Purification and Characterization of Light-Harvesting Chlorophyll a/b-Protein Complexes of Photosystem II from the Green alga, Bryopsis maxima

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Light-harvesting chlorophyll a/b-proteins of photosystem II (LHC II) were purified from thylakoid membranes of the green alga, Bryopsis mexima. Extraction with digitonin did not solubilize chlorophylls (Chl) and carotenoids to any significant extent. Two forms of purified LHC II, P4 and P5, with respective apparent particle sizes of 280 and 295 kDa, were obtained by sucrose density gradient centrifugation and column chromatography on DEAE-Toyopearl. P4 and P5 had similar spectral absorption at 77 K with Chl a maxima at 674, 658 and 438 nm and Chl b maxima at 649 and 476 nm. Carotene was not present in P4 or P5. Fluorescence excitation spectra demonstrated that Chl b, siphonaxanthin and siphonein can efficiently transfer absorbed light energy to Chl a. P4 and P5 each contained two apoproteins of 28 and 32 kDa, with similar but not identical amino acid compositions. P5 contained 6 molecules of Chl a, 8 of Chl b and 5 of xanthophyll (three molecules of siphonaxanthin and one each of siphonein and neoxanthin) per polypeptide.