THE STRUCTURES OF S-0 SPHEROIDENE IN THE LIGHT-HARVESTING (LH2) COMPLEX AND S-0 AND T-1 SPHEROIDENE IN THE REACTION-CENTER OF RHODOBACTER-SPHAEROIDES-2.4.1 AS REVEALED BY RAMAN-SPECTROSCOPY

The Raman spectrum of S-0 spheroidene in the light-harvesting (LH2) co mplex (LHC) and those of S-0 and T-1 spheroidene in the reaction cente r (RC) of Rhodobacter sphaeroides 2.4.1 were recorded. Comparison of t he So Raman spectrum of the all-trans isomer bound to the LHC of R. sp haeroides 2.4.1 with that free in n-hexane solution suggests that the LHC-bound carotenoid takes a fiat, all-trans configuration with possib le distortion in the plane of the conjugated chain. On the other hand comparison of the So Raman spectrum of the 15-cis isomer bound to the RC with that free in n-hexane solution suggests that the RC-bound caro tenoid takes a 15-cis configuration which is twisted around the C15=C1 5' bond and distorted in the -C15H=C15'H- plane. The T-1 Raman spectra of the RC-bound spheroidene indicated substantial twisting and in-pla ne distortion of the conjugated backbone. Based on the above results, a mechanism of triplet-energy dissipation by the RC-bound carotenoid, which involves an internal rotation around the C15=C15' bond, is propo sed. (C) 1996 John Wiley & Sons, Inc.