Effect of deletion of Rpe65 and Grk1 on opsin phosphorylation. Retinae of cyclic-light-reared 2-month-old WT, Rpe65−/−, Grk1−/−, and Rpe65−/−Grk1−/− mice were homogenized in 8 M urea and digested with endoproteinase Asp-N in 10 mM Tris buffer at pH 7.6 to cleave the opsin C-terminus, which were analyzed online with a LCQ mass spectrometer. In the Grk1−/− and Rpe65−/−Grk1−/− mice, no significant opsin phosphorylation was observed. White bars, animals exposed to room light for 6 hours; black bars, animals dark-adapted for 12 hours. Data are shown as the percentage of rhodopsin C-terminus containing phosphorylation, independent of the multiplicity of phosphorylation, and presented as mean ± SEM; n=3.