Characterization of fly rhodopsin kinase

Rhodopsin kinase activity of Musca domestica was characterized in a reconstitution assay, using urea‐treated eye membranes as substrate and a purified fraction of eye cytosol as the enzyme. Analysis of kinase activity in fly eye, brain and abdomen extracts by reconstitution assays revealed that fly rhodopsin kinase is an eye‐specific enzyme. It preferentially phosphorylates the light‐activated form of rhodopsin (metarhodopsin) and has little activity with other protein substrates. Rhodopsin kinase binds to metarhodopsin and is released from rhodopsin‐containing membranes. Metarhodopsin is a poor substrate for kinases from tissues other than the eye, making it a unique substrate for rhodopsin kinase. Rhodopsin kinase is inhibited by heparin, but not by the protein inhibitor of cAMP‐dependent protein kinase. Its K_m for ATP is 9 μM. Since fly rhodopsin is coupled to phospholipase C, studies of the interaction of rhodopsin with rhodopsin kinase can be useful in analysis of the reactions that lead to termination of the inositol‐phospholipid‐signaling pathway.