Low-temperature spectroscopy of monomeric and trimeric forms of reconstituted light-harvesting chlorophyll a/b complex

Low-temperature (polarized) light spectroscopy was used to study reconstituted light-harvesting complex (LHCII) of Photosystem II, both in the monomeric and trimeric form. Monomeric LHCII was reconstituted from the apoprotein overexpressed in Escherichia coli and pigments were extracted from chloroplast membranes and subsequently separated from unbound pigments on an anion-exchange column. These monomers trimerize in the presence of a lipid fraction isolated from thylakoids or of pure phosphatidylglycerol. The spectroscopic properties are compared to those of monomeric and trimeric forms of native LHCII and many similarities exist. However, these reconstituted complexes seem to contain slightly fewer chlorophylls, whereas one pigment that is a chlorophyll a in native LHCII is replaced by a chlorophyll b in reconstituted LHCII.