ABSTRACT
This chapter reviews the knowledge of visual transduction in the rod photoreceptors and its regulation by phosphorylation of rhodopsin. Phototransduction in the vertebrate rod visual cell is a process that begins with light absorption by rhodopsin in the disk membrane and results in the hyperpolarization of the plasma membrane. Except in the basal area of the outer segment, the disk membrane and outer segment plasma membrane are not connected; that is, light absorption and hyperpolarization occur in different membranes. The primary structure of bovine and shee rhodopsins was determined by analysis of amino acid sequences and that of human and fruitfly rhodopsins by sequencing of genomic and cDNA clones encoding membrane proteins. Protein modifications play an important role in determining the function and fate of many proteins. Posttranslational modifications include partial proteolysis, glycosylation, sulfation, and phosphorylation. The inner and outer segments of the rod photoreceptor are different, not merely in morphology, but also in electro physiologic activity.
