A Spectroscopic Study of a Photosystem I Antenna Complex
The unusual long wavelength fluorescent behavior of Photosystem I (PSI) has been well documented (1) This study investigates the origin and temperature dependence of this emission using an intact peripheral antenna preparation isolated from a PSI complex originally extracted from spinach. This antenna complex (LHCP-I) contains polypeptides in the 19–24 kDa range and exhibits a red shift in emission maximum from 685nm (F685) to 735nm (F735) as the temperature is lowered. Fluorescence excitation spectra demonstrate that chlorophyll b (chl b) preferentially stimulates the long wavelength emission at both room temperature and 77K and also indicate the presence of a long wavelength absorber in the 703–708nm range. Excitation polarization scans show a rising polarization value reaching a maximum of 0.3 from 705nm to 725nm, confirming the presence of a long wavelength pigment or pigments which are primarily responsible for emission at 735nm (F735). Absorption spectra demonstrate that this species comprises a small percentage of the total pigment population in the light harvesting antenna. The overall fluorescence yield of the complex increases as the temperature is lowered suggesting the presence of a quenching mechanism which does not involve the reaction center, P700.
KeywordsReaction Center Excitation Spectrum Fluorescence Yield Antenna Complex Fluorescence Excitation Spectrum
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- 2.Mukerji, I. and Sauer, K. (1989) in Photosynthesis (Briggs, W.H., ed.) A.R. Liss, New York in press.Google Scholar