title: Purification and characterization of S-modulin, a calcium-dependent regulator on cGMP phosphodiesterase in frog rod photoreceptors.
abstract: S-modulin is a 26 kDa protein that regulates light sensitivity of cGMP phosphodiesterase in a Ca(2+)-dependent manner in frog rod outer segments (ROSs). In the present study, we purified S-modulin by taking advantage of a hydrophobic interaction between Phenyl Sepharose and S-modulin at high Ca2+ concentrations. The yield was greater than 90%. 45Ca(2+)-binding experiment showed that S-modulin is a Ca(2+)-binding protein. At high Ca2+ concentrations, S-modulin binds to ROS membranes. The binding target of the Ca2+/S-modulin complex is possibly a ROS membrane lipid(s), but it was difficult to identify. The binding was observed mainly at greater than 1 microM Ca2+. The amino acid sequence deduced from proteolytic fragments of S-modulin was approximately 80% and 60% identical to those of recovering and visinin, respectively.
authors.affiliation: Department of Physiology, Keio University School of Medicine, Tokyo, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kawamura
authors.forename: K
authors.initials: K
authors.lastname: Takamatsu
authors.forename: K
authors.initials: K
authors.lastname: Kitamura
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D005136:Eye Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D051597:Hippocalcin; D008074:Lipoproteins; D008081:Liposomes; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009419:Nerve Tissue Proteins; D011892:Rana catesbeiana; D051603:Recoverin; D012374:Rod Cell Outer Segment / Q000201:enzymology*; D012689:Sequence Homology, Nucleic Acid
chemical_list: D002135:Calcium-Binding Proteins; D005136:Eye Proteins; D008074:Lipoproteins; D008081:Liposomes; D009419:Nerve Tissue Proteins; D051603:Recoverin; D051597:Hippocalcin; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D002118:Calcium