Arrestin of bovine photoreceptors reveals strong ATP binding

The soluble protein arrestin (also named 48K-protein or retinal-S-antigen) is involved in controlling light-dependent transducin and cGMP phosphodiesterase activity in retinal rods. It is also known for its ability to induce autoimmune reactions in the eye causing the eye disease uveitis. We report here a rapid binding of ATP to arrestin with KA = 2 x 10(21) (l/mol)3 and a coordination number n = 3. This ATP binding to arrestin supports the notion of a nucleotide exchange which initiates the rapid inhibitory action of this enzyme during the primary step of vertebrate phototransduction.