Changes of absorption spectra during heat-induced denaturation of Photosystem II core antenna complexes CP43 and CP47: revealing the binding states of chlorophyll molecules in these two complexes

The Photosystem II (PSII) core antenna complexes, CP43 and CP47, were prepa red from spinach (Spinacia oleracea L.). The absorption spectra in the red region at room temperature were recorded for the PSII core antenna samples after increased temperature treatment (up to 80 degreesC). Derivative and d ifference spectra revealed the existence of two groups of chlorophyll a (Ch l a) molecules in both CP43 and CP47. The one with the absorption peak in t he shorter wavelength region was designated as CP43-669 and CP47-669, while the other with the absorption peak in the longer wavelength region was des ignated as CP43-682 and CP47-680. The results of the thermal treatment expe riment demonstrated that CP43-669 and CP47-669 may exist as monomers of Chl a and that their binding sites on the polypeptides are insensitive to ther mal treatment, whereas CP43-682 and CP47-680 may exist as dimers or multime rs of Chl a and their binding regions in the polypeptide chains are more se nsitive to heat treatment. The excitation energy transfer mechanism between these two different groups of Chl a molecules is also analyzed. (C) 2001 E lsevier Science B.V. All rights reserved.