INTERACTION OF MG(II), CA(II) AND MN(II) IONS WITH THE LIGHT-HARVESTING PROTEINS OF CHLOROPLAST THYLAKOID MEMBRANES STUDIED BY FT-IR DIFFERENCE SPECTROSCOPY
A. Ahmed et Ha. Tajmirriahi, INTERACTION OF MG(II), CA(II) AND MN(II) IONS WITH THE LIGHT-HARVESTING PROTEINS OF CHLOROPLAST THYLAKOID MEMBRANES STUDIED BY FT-IR DIFFERENCE SPECTROSCOPY, Journal of molecular structure, 319, 1994, pp. 145-151
The interaction of Mg(II), Ca(II) and Mn(II) ions with the light-harve
sting (LHC-II) proteins of chloroplast thylakoid membranes was investi
gated in aqueous solution at different metal ion concentrations (0.01-
20 mM), using Fourier transform-infrared (FT-IR) difference spectrosco
py. The infrared difference spectroscopic results for the amide I and
amide II regions (1800-1500 cm-1) have shown a strong metal-protein in
teraction at high metal ion concentrations (5-20 mM), whereas at very
low concentrations (0.01-1 mM) the metal cation binding is negligibie.
The metal ion binding is mainly via the protein carbonyl group at low
cation concentration, whereas metal ion coordination to the protein C
=O and C-N groups were observed at higher cation concentrations. The M
n-tyrosine binding was also observed at high metal ion concentrations.
Major conformational changes from alpha-helix (48% in uncomplexed pro
tein) to beta-sheet and turn structures were observed in the presence
of these metal cations at high concentrations (10-20 mM).