Characterization Of Carotenoid Triplet States In The Light-Harvesting Complex 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 absorption-detected magnetic resonance in zero magnetic field (ADMR) spectroscopy, Detailed HPLC analysis of carotenoids from B800-850 demonstrated the presence of several carotenoids bound to the complex: the major ones are hydroxyspheroidene and spheroidene (together 80%), followed by neurosporene and hydroxyneurosporene (7%), sphereidenone and hydroxyspheroidenone (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 chosen 2\E\ transitions of carotenoids indicated that all these triplet states can be attributed to three different populations of one carotenoid family, probably to spheroidene and to hydroxyspheroidene, with different out-of-plane distortions of their polyene chain due to a different protein environment. Triplet states of the neurosporene and the spheroidenone families are probably not observed because of the low signal amplitude.