PICOSECOND DYNAMICS OF EXCITATIONS IN LIGHT-HARVESTING COMPLEX B800-850 FROM CHROMATIUM-MINUTISSIMUM STUDIED USING FLUORESCENCE SPECTROCHRONOGRAPHY

The picosecond dynamics of excitations in the isolated B800-850 light- harvesting complex of the purple sulfur bacterium Chromatium minutissi mum has been studied using picosecond fluorescence spectrochronography . A short-lived component of about 20 ps lifetime has been found at 77 K at the short wavelength part of the B850 fluorescence spectrum simil ar to that previously described for the core antenna bacteriochlorophy ll band B880 of Rhodospirillum rubrum. Evidence has been presented ind icating that this component is likely to reflect excitation energy rel axation step(s) involving both photoexcited bacteriochlorophyll and th e protein environment. A new kinetic scheme of excitation transfer fro m the peripheral antenna to the photoreceptor units in purple bacteria is suggested which takes into account these findings.