Electrochromic spectral band shift of carotenoids in the photosynthetic membranes of Rhodospirillum molischianum and Rhodospirillum photometricum

Abstract

Light-induced and diffusion-potential-induced absorption changes of carotenoids were studied in two species of photosynthetic bacteria in the genus Rhodospirillum. In Rs. photometricum, illumination or inside-negative diffusion potentials elicited a red shift of the carotenoid spectrum. However, in Rs. molischianum the spectral shift was in the opposite direction: i.e., a blue shift. The major carotenoids in both species were lycopene and rhodopin. The opposite shift direction can be explained by an opposite polarity of the permanent fields around the carotenoid molecules, which probably originates from the surrounding polypeptides.