title: Characterization of regulatory light chain-a myosin kinase from smooth muscle of scallop, Patinopecten yessoensis.
abstract: The protein kinase that phosphorylates the regulatory light chain-a (RLC-a) of scallop smooth muscle myosin was isolated from scallop smooth muscle (Sohma, H. & Morita, F. (1986) J. Biochem. 100, 1155-1163). The enzymatic properties of this kinase (aMK) were investigated using RLC-a as the substrate. The Km value for ATP was 6.5 microM in the presence of 27 microM RLC-a at pH 7.0, and that for RLC-a was 133 microM in the presence of 1 mM ATP. The Vm value at saturation of both RLC-a and ATP was 0.25 s-1 at pH 7.0. The pH activity curve for aMK was bell-shaped with a maximum at around pH 7.8. The aMK activity was inhibited strongly by an increase in the KCl concentration. aMK required Mg2+, but was inhibited by high concentrations of Mg2+. The optimum activity was seen at 3 mM MgCl2. The mode of inhibition of the aMK activity by Ca2+ was studied. Assuming that the binding of Ca2+ to aMK induces the inhibition, the dissociation constant of Ca2+ was estimated to be 64 microM. aMK also phosphorylated LC20 of chicken gizzard myosin at a similar rate to that for RLC-a and the DTNB light chain of rabbit skeletal muscle myosin at a more lower rate. The helix and beta-sheet contents of aMK were estimated to be 19 and 30%, respectively, from the CD spectrum.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D008974:Mollusca / Q000201:enzymology*; D009130:Muscle, Smooth / Q000201:enzymology; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors / Q000302:isolation & purification* / Q000378:metabolism; D010766:Phosphorylation; D013056:Spectrophotometry, Ultraviolet
chemical_list: D009219:Myosin-Light-Chain Kinase