Heterogeneity of the main light-harvesting chlorophyll a/b-protein complexof photosystem II (LHCII) at the level of trimeric subunits

To study organization of the main light-harvesting chlorophyll a/b-protein complex of photosystem II (LHCII) from spinach thylakoid membranes at the l evel of trimeric subcomplexes, we have applied non-denaturing isoelectric f ocusing (ndIEF) in vertical, slab polyacrylamide gels. When analyzed by two consecutive ndIEF/electroelution runs, spinach BBY membrane preparations ( PSII,enriched, stacked thylakoid membranes) were resolved into nine fractio ns of 100% purity, labelled 1-9 in order of decreasing pl values. Seven of these fractions (3-9) were shown by absorption spectroscopy to stand for LH CII subcomplexes. The subcomplexes were established - by monitoring their c ircular dichroism spectra and comparing them to the spectra of native LHCII trimers, and monomers - to be structurally intact trimers. The analysis of polypeptide composition of the subcomplexes in terms of apparent molecular masses and Lhcb genes' products led us to the conclusion that each of the subcomplexes might be a mixed population of closely similar individual trim ers, comprising of permutations of Lhcb1 and Lhcb2 (subcomplexes 3-7) or Lh cb1, Lhcb2 and Lhcb3 (subcomplexes 8 and 9). (C) 2001 Elsevier Science B.V. All rights reserved.