IDENTIFICATION OF THE 48-K PROTEIN THAT INTERACTS WITH ILLUMINATED RHODOPSIN IN VERTEBRATE RETINAL RODS WITH THE RETINAL S-ANTIGEN INDUCING EXPERIMENTAL AUTOIMMUNE UVEORETINITIS
In vertebrate retinal rod outer segments, a soluble 48 K [kilodalton] protein binds to disk membranes upon illumination in presence of ATP or GTP. Its binding to photoexcised rhodopsin implies a probable role of the 48 K protein in the ATP dependent regulation of the photoinduced enzymatic cascade which controls the hydrolysis of cGMP. The retinal S antigen is also a soluble protein located in photoreceptor cells which is known to be an organ-specific auto-antigen inducing experimental autoimmune uveoretinitis. Using extracts of purified cattle and frog rod outer segments, purified bovine S antigen, and monoclonal antibodies gainst S antigen, both proteins exhibited identical characteristics with respect to their migration in sodium dodecyl sulfate-gel electrophoresis, their binding to rod disc membranes upon illumination in presence of ATP or GTP, and their immunological reactivity with monoclonal antibodies.