Spectroscopic characterization of the low-light B800–850 light-harvesting complex of Rhodopseudomonas palustris, strain 2.1.6

Abstract

The low-light B800–850 antenna-complex from Rhodopseudomonas palustris has been studied using polarized-light and time-resolved spectroscopy. The low-light B800–850 complex from Rps. palustris is compared with its high-light B800–850 equivalent from the same species, and with the B800ndash;850 complex from Rhodobacter sphaeroides. The comparison shows that the B850 component of all these light-harvesting complexes is very similar, indicating a conserved arrangement of the bacteriochlorophyll molecules contributing to this band. However, the B800 component of these light-harvesting complexes is rather different. In contrast to the B800–850 of Rb. sphaeroides, the low-light B800–850 complex of Rps. palustris shows strong exciton splitting of the B800 band as manifested by the low-temperature circular-, linear dichroism and polarized fluorescence spectra in the 800 nm spectral region. Moreover, picosecond absorption recovery measurements indicate that fast excitation energy transfer processes take place within the 800 nm band before transfer to B850 occurs. The results are explained by the increased B800 pigment density in the low-light B800–850 complex, resulting in relatively strong bacteriochlorophyll (BChl) a-BChl a interactions.