MICROSCOPIC AND SPECTROSCOPIC STUDIES OF UNTREATED AND HEXANOL-TREATED CHLOROSOMES FROM CHLOROFLEXUS-AURANTIACUS

When isolated chlorosomes from Chloroflexus aurantiacus are treated wi th 1-hexanol, the BChl c Q(y) absorption band shifts from 740 to 670 n m, while the baseplate BChl a remains at 795 nm. The relative amount o f BChl c in the 740 and 670 nm forms depends on the hexanol concentrat ion. Atomic force microscopy was used to study the ultrastructure of n ative, hexanol-treated, and protein-free chlorosomes. Chlorosomes appe ared to be larger and more rounded upon hexanol treatment and did not return to the original shape or size after 2-fold dilution. Therefore, the hexanol treatment is not completely reversible in terms of chloro some structure. Untreated, hexanol-treated and and hexanol-treated and then diluted samples were investigated using steady-state and time-re solved fluorescence spectroscopy. For the sample treated with 68 mM he xanol, a 24 ps energy transfer from BChl c to a was observed in the pi cosecond fluorescence measurements. After 2-fold dilution, most of the kinetic properties of the untreated chlorosomes, characterized by a m ajor energy transfer component of 15 ps from BChl c 740 to BChl a 795, were regained. Energy transfer from either BChl c 740 or BChl c 670 t o baseplate BChl a is fast and relatively efficient in untreated chlor osomes. In hexanol-treated chlorosomes, the excited state lifetime is not very different from that in untreated samples, but the energy tran sfer efficiency is quite low. This may result from concentration quenc hing of the monomeric pigments in the hexanol-treated chlorosomes.