DIRECT ZINC-BINDING TO PURIFIED RHODOPSIN AND DISK MEMBRANES

Using the radionuclide Zn-65, we have demonstrated the direct binding of zinc to purified rhodopsin. Zn-65 in eluted with detergent-solubilized rhodopsin from concanavalin A columns and remains bound to the visual pigment through a subsequent gel-filtration step. Zinc binding to purified disc membranes is highly specific and, of the ions tested, copper is the best competitor. Equilibrium-dialysis experiments indicate that zinc binding to detergent-solubilized forms of rhodopsin may increase on bleaching the photopigment. These results may have important implications for studies that indicate that zinc plays a role in retinal degeneration and normal photoreceptor physiology.