Excitation Energy Transfer in Living Cells of the Green Bacterium Chlorobium Limicola Studied by Picosecond Fluorescence Spectroscopy

Abstract

During the past few years advances have been made in understanding the structure and the function of the photosynthetic unit (PSU) of green bacteria (Olson, 1980; Fetisova and Borisov, 1960; Betti et al., 1962; Wechsler et al., 1964; flmesz, 1965; Zuber, 1965; Amesz and Vasmel, 1986; van Dorssen et al., 1986a,b; Fetisova et al., 1966; Fetisova et al., 1967). In these studies the progress of preparative biochemistry proved to be decisive, since a major reason for the paucity of data on the primary events in the photosynthesis of green bacteria was undoubtedly the large antenna. The available data provide information about the structure and function of various isolated subcellular pigmented fractions from green bacteriaj whereas hardly anything is known about the functioning of the PSU in intact cells under physiological conditions. Because of their large antenna size (largest of alt the known PSUs) and the high quantum yield of primary charge separation in the reaction center (RC) (Fetisova and Borisov, 1960) this family of organisms is most promising (Fetisova and Fok, 1964) in the search for the fundamental principles of the PSU structural organization which provide large and highly efficient PSUs in vivo. This work presents the results of the first direct measurements of picosecond excitation energy transfer rates within a light-harvesting antenna in living cells of the green bacterium Chlorobium limicola as welt as the results of the investigation of some structural aspects of this energy transfer.