THE B800-850 COMPLEX OF THE PURPLE BACTERIUM CHROMATIUM-TEPIDUM - LOW-TEMPERATURE ABSORPTION AND STARK SPECTRA

Low-temperature absorption and Stark-effect spectra of the B800-850 co mplex of Chromatium (C.) tepidum are presented. The low-temperature ab sorption shows two bands with about equal amplitude. centred at about 795 nm and at about 808 nm. The Stark spectrum of the complex is simil ar to the Stark spectrum from LH2 complexes from other bacteria. with additional structure around 800 nm. The BChls absorbing at 850 nm poss ess a difference dipole moment \Delta<(mu)over right arrow>\ of about 4.3-5.3 D f(-1). The two absorbing species in the 800 nm band give ris e to a completely different Stark effect. the 808 nm band having \Delt a<(mu)over right arrow>\ = 1.3-1.6 D f(-1) similar to that of the B800 band of Rhodopseudomonas acidophila, whereas the 795 band has a much larger \Delta<(mu)over right arrow>\ (3.6-4.5 D f(-1)). It is suggeste d that the B800 pigments in LH2 of C, tepidum are present in two forms , which differ in the orientation of their optical Q(y)-transition mom ents. (C) 1998 Elsevier Science B.V. All rights reserved.