POLARIZED SITE-SELECTION SPECTROSCOPY OF CHLOROPHYLL-A IN DETERGENT

Monomeric chlorophyll a (Chl a) was obtained from the isolated core an tenna complex CP47 of photosystem II after incubation with the deterge nt triton X-100 and was studied by low-temperature polarized light spe ctroscopy with the aim to obtain model spectra for Chl a in intact pho tosynthetic complexes. Evidence is presented by circular dichroism and anisotropy measurements that the isolated chlorophyll is monomeric. T he absorption bandwidths are relatively large compared to those found in photosynthetic complexes due to inhomogeneous broadening introduced by the detergent. By selective laser excitation at low temperature, c onsiderable narrowing can be achieved. A number of vibrational bands a re resolved in the site-selected, polarized absorption and fluorescenc e emission spectra. The emission spectrum of Chl a in detergent-damage d CP47 is compared with that of Chl a in the intact light-harvesting c omplex of photosystem II (LHC-II) from green plants. The spectra are r emarkably similar indicating that the low-temperature thermal emitter in LHC-II has spectral properties that are very similar to those of mo nomeric Chl a.