Mechanistic studies on the phosphorylation of photoexcited rhodopsin

The mechanism of the photophosphorylation of rhodopsin was studied using several synthetic peptides corresponding to the sequence of the phosphorylation domain. It was found that the decapeptide (residues 339-348) was effectively phosphorylated by rhodopsin kinase only when incubation was performed in the presence of both rhodopsin and light. These results are interpreted to suggest that in the dark-adapted state rhodopsin kinase exists in an inactive conformation and that this is converted into a catalytically competent form only after interaction with metarhodopsin II (Rho*).