Abstract
Abstract The interaction of Mg(II), Ca(II) and Mn(II) ions with the light-harvesting (LHC-II) proteins of chloroplast thylakoid membranes was investigated in aqueous solution at different metal ion concentrations (0.01–20 mM), using Fourier transform-infrared (FT-IR) difference spectroscopy. The infrared difference spectroscopic results for the amide I and amide II regions (1800–1500 cm −1 ) have shown a strong metal—protein interaction at high metal ion concentrations (5–20 mM), whereas at very low concentrations (0.01–1 mM) the metal cation binding is negligible. The metal ion binding is mainly via the protein carbonyl group at low cation concentration, whereas metal ion coordination to the protein CO and CN groups were observed at higher cation concentrations. The Mn—tyrosine binding was also observed at high metal ion concentrations. Major conformational changes from α-helix (48% in uncomplexed protein) to β-sheet and turn structures were observed in the presence of these metal cations at high concentrations (10–20 mM).
Published Version
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