Amino acid residues controlling the properties and functions of rod and cone visual pigments.

The visual transduction processes in rod and cone photoreceptor cells are initiated by photon absorption by the different types of visual pigments. In relation to the functional difference between these cells, cone visual pigments in chicken retinas exhibit faster regeneration from 11-cis-retinal and opsin and faster decay of physiologically active intermediate (Meta II) than rod visual pigment, rhodopsin. Replacement of the amino acid residue at position 122 of chicken rhodopsin by the residues present in the respective cone pigments dramatically changes both the decay rate of Meta II and the rate of regeneration into those of the cone pigment-type, indicating that the residue at this position is a major determinant controlling these properties. Thus, the single replacement of amino acid residue at this position would be one of the key steps of the divergence into twilight and daylight vision.