Comparative Study of Photochemistry of Microbial Rhodopsins (Type I) and Animal’s Rhodopsins (Type II)
The light-sensitive proteins, rhodopsins, are present in all the kingdoms of living organisms. Type I (microbial) rhodopsins generally have a photoenergetic function; most type II rhodopsins are photoreceptor proteins of animals. The paper presents a comparison of the spectral characteristics and photochemical reactions of three different rhodopsins: bacteriorhodopsin of the halophilic archaeon H. salinarum, rhodopsin of the soil psychrotrophic bacterium E. sibiricum, and visual rhodopsin of bovine rods. Stationary absorption of the proteins, parameters of their photochemical reactions, such as the rate of isomerization of retinal chromophore, and the formation of the first products, as well as the probability of reverse photoreaction and the presence of spontaneous thermal isomerization of retinal are considered. It is assumed that, in the course of evolution, the mechanism of interaction of retinal with the protein in the chromophore center of animal visual rhodopsins (type II rhodopsins) as photoinformation proteins has become more perfect and specific.