A QUANTITATIVE-ANALYSIS OF PROTEIN SECONDARY STRUCTURE OF PHOTOSYSTEM-II PARTICLES AND LIGHT-HARVESTING COMPLEX OF CHLOROPLAST THYLAKOID MEMBRANES BY FT-IR SPECTROSCOPY

We report the preliminary results of protein conformational analysis o f photosystem II (PSII) particles and light-harvesting complex (LHC-II ) of chloroplast thylakoid membranes isolated from fresh spinach in aq ueous solution at neutral pH. FT-IR spectroscopy, with its self-deconv olution and second derivative resolution enhancement as well as curve- fitting procedures, was used in the amide I region (1700-1600 cm(-1)), to determine the amount of each conformation present in coexistence. Spectroscopic data have shown the domination of the alpha-helix (1656 cm(-1)) to be a major conformational component in both PSII (64%) and LHC-II (48%) systems. The beta-sheet (1626-1640 cm(-1)), with 17% for PSII and 21% for LHC-II, and the turn structure (1670-1680 cm(-1)), wi th 23% for LHC-II and 13% for PSII, with beta-antiparallel (1689-1691 cm(-1)) 8% for LHC-II and 6% for PSII, were the minor conformations pr esent in aqueous solution.