In this study, we address the mechanism of visual arrestin release from light-activated rhodopsin using fluorescently labeled arrestin mutants. We find that two mutants, I72C and S251C, when labeled with the small, solvent-sensitive fluorophore monobromobimane, exhibit spectral changes only upon binding light-activated, phosphorylated rhodopsin. Our analysis indicates that these changes are probably due to a burying of the probes at these sites in the rhodopsin-arrestin or phospholipid-arrestin interface. Using a fluorescence approach based on this observation, we demonstrate that arrestin and retinal release are linked and are described by similar activation energies. However, at physiological temperatures, we find that arrestin slows the rate of retinal release ϳ2-fold and abolishes the pH dependence of retinal release. Using fluorescence, EPR, and biochemical approaches, we also find intriguing evidence that arrestin binds to a post-Meta II photodecay product, possibly Meta III. We speculate that arrestin regulates levels of free retinal in the rod cell to help limit the formation of damaging oxidative retinal adducts. Such adducts may contribute to diseases like atrophic age-related macular degeneration (AMD). Thus, arrestin may serve to both attenuate rhodopsin signaling and protect the cell from excessive retinal levels under bright light conditions.The visual photoreceptor rhodopsin is perhaps the best model system for understanding the mechanisms used in Gprotein-coupled receptor (GPCR) 1 signaling, as detailed information exists on the structures and dynamic interactions of the protein constituents (1). Visual activation begins with absorption of light by the 11-cis-retinal chromophore in rhodopsin. The photoactivated form of rhodopsin, Rho* or "Meta II," interacts with and activates the G-protein transducin, which exchanges nucleotide and then diffuses to interact with downstream effectors. Signaling by Rho* is terminated by slow thermal decay and the release of retinal. Alternatively, signaling can be quickly terminated by a process that begins with phosphorylation of rhodopsin's C-terminal tail through the action of rhodopsin kinase (2, 3). The phosphorylated Rho* is then bound by arrestin, which stops signaling by physically occluding the G-protein binding site (4, 5).In the present study, we address how these two inactivation mechanisms are related and, specifically, what governs arrestin release from rhodopsin. Arrestin is known to bind to phosphorylated Meta II, a form in which the photolyzed chromophore all-trans-retinal is still attached to the receptor by a deprotonated Schiff base. Arrestin does not bind phosphorylated opsin, but all-trans retinal added exogenously can stimulate arrestin binding to phosphorylated opsin (6, 7). Early studies showed indirectly that retinal release and arrestin release are probably interrelated events (7,8). However, how these processes are linked or whether arrestin binds other photointermediates of rhodopsin (such as the storage form Meta III) is still unknown...