The Phosphorylation of Rhodopsin
Visual transduction in retinal photoreceptor cells results from a cascade of chemical reactions that translate a light signal into a hyperpolarization of the plasma membrane of the cell (reviewed by Stryer 1986; Chabre and Deterre 1989). The highly regulated reactions in this cascade are responsible for initiating, amplifying and quenching the light-induced electrical response. Three different proteins modulate the reactions by binding to the surface of metarhodopsin II during the course of photo-transduction: transducin, rhodopsin kinase, and arrestin. Transducin, a retina specific G-protein, is involved in amplifying the light signal; rhodopsin kinase and arrestin participate in quenching the light signal.
Light-induced phosphorylation of rhodopsin was detected independently in three laboratories (Bownds et al. 1972; Kühn & Dreyer 1972; Frank et al. 1973). Later, this reaction also was found to occur in vivo (Kühn 1974). The work of Hermann Kühn has greatly contributed to our understanding of the quenching mechanism of photolyzed rhodopsin. The group characterized many properties of rhodopsin kinase (McDowell & Kühn 1977; Kühn 1978; Wilden & Kühn 1982) and showed that phosphorylation alone is insufficient for quenching photolyzed rhodopsin. His laboratory also has shown that a second protein, arrestin, is required to inhibit phosphodiesterase and, thus, the entire phototransduction cascade (Kühn et al. 1984; Pfister et al. 1985; Wilden et al. 1986).
In this review, we will summarize our current work on the properties of rhodopsin kinase and the role of phosphorylation of rhodopsin.
KeywordsLight Signal Ribose Moiety Purine Ring Nucleotide Substrate Rhodopsin Kinase
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