CD spectroscopy provides evidence for excitonic interactions involving red-shifted chlorophyll forms in photosystem I

Selective destruction of the strongly dichroic redshifted chlorophyll form (C709 nm) in photosystem I (PSI) trimers from Spirulina, by either non-selective high intensity illumination (photobleaching) or incubation,vith low concentrations of Triton X-100 is accompanied by changes in the circular dichroism spectrum of the same amplitude and of opposite sign at 677 nm, The data are interpreted in terms of a dimeric chlorophyll structure with excitonic bands at these two wavelengths. Similar photobleaching experiments with PSI-2001 from maize also suggest the presence of bulk antenna/red form excitonic interactions. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.