POLARIZED SPECTRA OF ORIENTED PIGMENT-LIPOPROTEIN COMPLEXES FROM THE PURPLE BACTERIUM CHROMATIUM-MINUTISSIMUM

Polarized absorption, fluorescence and photoacoustic spectra of bacter iochlorophyll (BChl)-lipoprotein complexes from the purple bacterium C hromatium minutissimum oriented in stretched polyvinylalcohol films we re measured at room temperature and 85 K. The preparations contain lar ge amounts of the B800-820 antenna complexes. From polarized absorptio n spectra taken under various light beam incidence angles with respect to the film plane, conclusions concerning arrangement of pigment mole cules in B800-820 complex are obtained. The transition moments of the BChl Q(y) band are not exactly parallel to the membrane plane. It seem s that there are pools of differently oriented BChl chromophores absor bing in both 800 nm and 820 nm regions. Change in temperature strongly influences linear dichroism of carotenoids and BChl Q(x) bands. The r eversible changes in absorption, linear dichroism and photoacoustic sp ectra caused by the variation in sample temperature suggest strongly t he reversible twisting of carotenoid molecules, related probably to mo dification of the interactions between carotenoids and proteins. Vario us carotenoids exhibit different yield of thermal deactivation and thi s yield is also temperature dependent.