On the Molecular Mechanism for Light Capture in Rhodopsin and Phytochrome Systems

Abstract

The light-absorbing mechanisms of the fundamental systems of trigger photoreception in animals and plants are discussed, on the basis of our calculations performed in the last several years. It is examined that chromophores of rhodopsin and phytochrome are conveniently isolated from other chromophoric groups in order to utilize light as a trigger not as an energy source, and the models for possible photoisomerizations of a non-cyclic tetrapyrrole are presented. The roles of the conformational changes of chromoproteins and of the specific interaction between a chromophore and its associated protein moiety in the cooperative excitation of the systems are also discussed, and it is shown for the case of thermal equilibrium states that the cooperativity can be brought forth from the flexible configurational state of chromophore (indicating that the state is affected by the surrounding chromoproteins through the conformational changes and the specific interaction).