Characterization of three forms of light-harvesting chlorophyll a/b-protein complexes of photosystem II isolated from the green alga, Dunaliella salina

Abstract

Three forms of light-harvesting chlorophyll a/b-protein complexes of photosystem II (LHC II) were isolated from the thylakoid membranes of Dunaliella salina grown under different irradiance conditions. Cells grown under a low intensity light condition (80 μmol quanta m-2 s-1) contained one form of LHC II, LHC-L. Two other forms of LHC II, LHC-H1 and LHC-H2, were separated from the cells grown under a high intensity light condition (1,500 μmol quanta m-2 s-1). LHC-L and LHC-H1 showed an apparent particle size of 310 kDa and contained four polypeptides of 31, 30, 29 and 28 kDa. LHC-H2, with a particle size of 110 kDa, consisted of 30 and 28 kDa polypeptides. LHC-L contained 7.5 molecules of Chl a, 3.2 of Chl b and 2.1 of lutein per polypeptide, analogous to the content in higher plants. LHC-H1, with 5.6 molecules of Chl a, 2.5 of Chl b and 1.8 of lutein per polypeptide was similar to that in the green alga Bryopsis maxima. LHC-L and LHC-H1 maintained high efficiency energy transfer from Chl b and lutein to Chl a molecules. LHC-H2 showed a high Chl a/b ratio of 7.5 and contained 3.4 molecules of Chl a, 0.5 of Chl b and 1.4 of lutein per polypeptide. Chl b and lutein could not completely transfer the excitation energy to Chl a in LHC-H2.