title: Purification and characterization of rhodopsin kinase.
abstract: Rhodopsin kinase was purified to near homogeneity by affinity binding to light-exposed rod cell outer segment membranes, followed by DEAE-cellulose and hydroxyapatite chromatography. This resulted in a 1055-fold purification of highly active rhodopsin kinase with an overall recovery of 19%. Rhodopsin kinase is a single polypeptide chain with Mr = 67,000-70,000 as determined by gel filtration and SDS-PAGE. The kinetic parameters of the enzyme for freshly bleached rhodopsin are Km = 4 microM and Vmax = 700 nmol/min/mg whereas for ATP Km = 2 microM (which is a low value for kinases generally, and about 20 times lower than comparable measurements for a kinase of a similar type, the beta-adrenergic-receptor kinase (Benovic, J.L., Mayor, F. Jr., Staniszewski, C., Lefkowitz, R.J., and Caron, M.G. (1987) J. Biol. Chem. 262, 9026-9032). GTP, on the other hand, is a very poor substrate (Km = 1 mM, Vmax = 10 nmol/min/mg). Rhodopsin kinase is competitively inhibited by adenosine and its mono- and diphosphate derivatives, but not by most other adenosine derivatives. Based upon measurements with 28 nucleotide derivatives, the ATP-binding site of rhodopsin kinase appears to have more specific requirements than that for other kinases. Compounds such as cGMP, inositol trisphosphate, and others that change concentration during exposure of rod cells to light have only minor inhibitory effects on the kinase activity, with the exception of inositol monophosphate, which can activate the kinase about 20% at 50-100 microM. Rhodopsin kinase has been difficult to store with retention of activity, but can be successfully stored frozen at -20 degrees C in 20% adonitol.
authors.affiliation: Department of Ophthalmology, University of Florida, Gainesville 32610-0284.
authors.forename: K
authors.initials: K
authors.lastname: Palczewski
authors.forename: J H
authors.initials: JH
authors.lastname: McDowell
authors.forename: P A
authors.initials: PA
authors.lastname: Hargrave
mesh_terms: D000818:Animals; D002417:Cattle; D002845:Chromatography; D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D000242:Cyclic AMP / Q000494:pharmacology; D006152:Cyclic GMP / Q000494:pharmacology; D017886:Durapatite; D005136:Eye Proteins; D051606:G-Protein-Coupled Receptor Kinase 1; D006882:Hydroxyapatites; D007202:Indicators and Reagents; D007295:Inositol Phosphates / Q000494:pharmacology; D007700:Kinetics; D008970:Molecular Weight; D010786:Photoreceptor Cells / Q000201:enzymology*; D011494:Protein Kinases / Q000302:isolation & purification* / Q000378:metabolism; D012265:Ribonucleotides / Q000494:pharmacology; D012374:Rod Cell Outer Segment / Q000201:enzymology*
chemical_list: D005136:Eye Proteins; D006882:Hydroxyapatites; D007202:Indicators and Reagents; D007295:Inositol Phosphates; D012265:Ribonucleotides; D017886:Durapatite; D000242:Cyclic AMP; D011494:Protein Kinases; D051606:G-Protein-Coupled Receptor Kinase 1; D006152:Cyclic GMP