CHARACTERIZATION OF CAROTENOID TRIPLET-STATES IN THE LIGHT-HARVESTINGCOMPLEX B800-850 FROM THE PURPLE BACTERIUM RUBRIVIVAX-GELATINOSUS

The carotenoid triplet states in the light-harvesting complex B800-850 from purple bacterium Rubrivivax gelatinosus were characterized by ab sorption-detected magnetic resonance in zero magnetic field (ADMR) spe ctroscopy, Detailed HPLC analysis of carotenoids from B800-850 demonst rated the presence of several carotenoids bound to the complex: the ma jor ones are hydroxyspheroidene and spheroidene (together 80%), follow ed by neurosporene and hydroxyneurosporene (7%), sphereidenone and hyd roxyspheroidenone (7.5%) and two other minor carotenoids that could be 3,4-dihydrospheroidenone and 3,4-dihydrohydroxyspheroidenone (5.5%). Three triplet states originating from carotenoids present in the B800- 850 were observed, The identical T-S spectra recorded at selectively c hosen 2\E\ transitions of carotenoids indicated that all these triplet states can be attributed to three different populations of one carote noid family, probably to spheroidene and to hydroxyspheroidene, with d ifferent out-of-plane distortions of their polyene chain due to a diff erent protein environment. Triplet states of the neurosporene and the spheroidenone families are probably not observed because of the low si gnal amplitude.