EXCITATION-ENERGY TRANSFER IN THE GREEN PHOTOSYNTHETIC BACTERIUM CHLOROFLEXUS-AURANTIACUS - A SPECIFIC EFFECT OF 1-HEXANOL ON THE OPTICAL-PROPERTIES OF BASEPLATE AND ENERGY-TRANSFER PROCESSES

The effect of 1-hexanol on spectral properties and the processes of en ergy transfer of the green gliding photosynthetic bacterium Chloroflex us aurantiacus was investigated with reference to the baseplate region . On addition of 1-hexanol to a cell suspension in a concentration of one-fourth saturation, a specific change in the baseplate region was i nduced: that is, a bleach of the 793-nm component, and an increase in absorption of the 813-nm component. This result was also confirmed by fluorescence spectra of whole cells and isolated chlorosomes. The proc esses of energy transfer were affected in the overall transfer efficie ncy but not kinetically, indicating that 1-hexanol suppressed the flux of energy flow from the baseplate to the B806-866 complexes in the cy toplasmic membranes. The fluorescence excitation spectrum suggests a s pecific site of interaction between bacteriochlorophyll (BChl) c with a maximum at 771 nm in the rod elements and BChl a with a maximum at 7 93 nm in the baseplate, which is a funnel for a fast transfer of energ y to the B806-866 complexes in the membranes. The absorption spectrum of chlorosomes was resolved to components consistently on the basis, i ncluding circular dichroism and magnetic circular dichroism spectra; b esides two major BChl c forms, bands corresponding to tetramer, dimer, and monomer were also discernible, which are supposed to be intermedi ary components for a higher order structure. A tentative model for the antenna system of C. aurantiacus is proposed.