ENERGY-STORAGE IN THE PRIMARY PHOTOPRODUCT OF VISION

We present a Car-Parrinello nb-initio molecular dynamics study of rhod opsin, the membrane protein responsible for the first step in vision. The ground state structures of the retinylidene chromophores of rhodop sin and of its primary photoproduct, bathorhodopsin, have been calcula ted with a simulated annealing procedure. In bathorhodopsin, the energ y 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 interactio ns in the energy storage mechanism are discussed. An analysis of the H OMO and LUMO charge distributions in rhodopsin and bathorhodopsin has been performed.