Molecular, enzymatic and functional properties of rhodopsin kinase from rat pineal gland

Rhodopsin kinase activity from rat pineal gland and from rat retina are indistinguishable, based upon determination of a variety of enzymatic and molecular properties. Both activities are independent of calcium, cyclic nucleotides, and calmodulin. Both are activated by spermine and inhibited by adenosine and some rhodopsin kinase specific adenosine derivatives such as sangivamycin. The Km's for rhodopsin, ATP, and GTP are indistinguishable for the protein kinase in extracts from the retina and from the pineal gland. The apparent molecular weight of the kinase from both sources, as determined by gel filtration and autoradiography of the 32P-labeled autophosphorylated kinase, is about 70 kDa. Rhodopsin kinase activity from pineal binds in a light-dependent manner to rhodopsin in rod outer segments as does the enzyme from retina. Monoclonal antibodies against bovine rhodopsin were used in an immunochemical study that identified a rhodopsin-immunoreactive protein in rat pineal gland and retina. Using an ELISA we demonstrated the presence of a rhodopsin-immunoreactive protein in rat pineal gland equivalent to 0.075 pmol rhodopsin per gland. Frog pineal organ (Rana catesbiana) contains 33 times more of this rhodopsin-like protein than does rat pineal gland.