title: Eye diseases and proteins controlling visual transduction.
abstract: Retinal S antigen is a soluble protein found in abundance in photoreceptor cells. Immunization of laboratory animals with this antigen in adjuvant induces experimental autoimmune uveoretinitis. Cellular immunity plays a major role in this condition. Autoimmune responses toward retinal S antigen are often observed in patients with retinal inflammatory disease, however, these responses are usually secondary to local tissue damage. The S antigen is identical to the 48 K protein characterized in rod outer segments by its light-dependent binding to the disk membrane in the presence of ATP. This protein binds specifically to photoexcited and phosphorylated rhodopsin, and quenches the activity of the light-dependent cGMP-phosphodiesterase, most probably because it competes with transducin. There is no evidence for any direct inactivation of phosphodiesterase by 48 K protein. In view of the numerous similarities between the photoreceptor enzyme cascade and hormone-activated cyclase systems, a related protein could be involved in the desensitization of hormonal systems.
mesh_terms: D000818:Animals; D000941:Antigens / Q000302:isolation & purification*; D019393:Arrestin; D005128:Eye Diseases / Q000276:immunology*; D005136:Eye Proteins / Q000302:isolation & purification*; D006801:Humans; D051381:Rats
chemical_list: D000941:Antigens; D019393:Arrestin; D005136:Eye Proteins