Configuration of the carotenoid in the reaction centers of photosynthetic bacteria. (2) Comparison of the resonance Raman lines of the reaction centers with those of the 14 different cis-trans isomers of β-carotene

Abstract

The Raman lines of the carotenoid in the reaction centers of Rhodopseudomonas spheroides 2.4.1 and G1C were compared to those of the 14 different configurational isomers of β-carotene. The isomers include the all-trans; 7-cis; 9-cis; 13-cis; 15-cis; 9-cis,13-cis; 9-cis,15-cis; 9-cis,13'-cis; and 13-cis,15-cis isomers, the configurations of which have been determined, as well as five isomers with unknown configurations. The isomers were isolated by means of HPLC after thermal isomerization of the all-trans isomer. Comparison of the C=C stretching frequencies in the 1570-1520 cm -1 region as well as of the spectral patterns in the 1300-1100 cm -1 region (the C-C stretching lines predominate) led us to an assignment of the configuration of the carotenoid in the reaction centers to 15-czs, which is in accord with our previous conclusion (Y. Koyama, M. Kito, T. Takii, K. Saiki, K. Tsukida and J. Yamashita, Biochim. Biophys. Acta (1982) 680, 109-118). Electronic absorption spectra of the isomers of β-carotene also were recorded and used as additional criteria for predicting the configuration of the carotenoid in the reaction centers.