Energy Storage in the Primary Photoproduct of Vision

We present a Car−Parrinello ab-initio molecular dynamics study of rhodopsin, the membrane protein responsible for the first step in vision. The ground state structures of the retinylidene chromophores of rhodopsin and of its primary photoproduct, bathorhodopsin, have been calculated with a simulated annealing procedure. In bathorhodopsin, the energy is primarily stored in distortions of the conjugated backbone of the chromophore, which presents a highly strained all- trans configuration. The roles of steric and electrostatic chromophore−protein interactions in the energy storage mechanism are discussed. An analysis of the HOMO and LUMO charge distributions in rhodopsin and bathorhodopsin has been performed.