title: Ruthenium red inhibits the binding of calcium to calmodulin required for enzyme activation.
abstract: The Ca(2+)-calmodulin (CaM)-dependent activation of myosin light chain kinase is inhibited by ruthenium red competitively with respect to Ca2+, with a Ki value of 8.6 microM. The binding of Ca2+ to CaM is inhibited by micromolar concentrations of ruthenium red. In the absence of Ca2+, CaM has two binding sites for ruthenium red with the dissociation constants of 0.36 and 8.7 microM, respectively. Ca2+ antagonizes the binding of ruthenium red to the low-affinity site on CaM. Binding of ruthenium red to the high-affinity site is not affected by Ca2+. The low- and high-affinity sites for ruthenium red are shown to be located in the NH2-terminal half and the COOH-terminal half of CaM, respectively. Lower concentrations of ruthenium red are needed for enzyme inactivation than for the dissociation of enzyme-CaM-Sepharose complex, suggesting these events have different Ca2+ requirements. Moreover, ruthenium red inhibits Ca(2+)-induced contraction of depolarized vascular smooth muscle in a competitive manner with respect to Ca2+. These results suggest that ruthenium red may be a new type of CaM antagonist that inhibits the binding of Ca2+ to CaM and thereby inhibits Ca(2+)-CaM-dependent enzymes and smooth muscle contraction competitively with respect to Ca2+.
authors.affiliation: Department of Molecular and Cellular Pharmacology, Mie University School of Medicine, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Sasaki
authors.forename: M
authors.initials: M
authors.lastname: Naka
authors.forename: F
authors.initials: F
authors.lastname: Nakamura
authors.forename: T
authors.initials: T
authors.lastname: Tanaka
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002417:Cattle; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism*; D011817:Rabbits; D012430:Ruthenium Red / Q000494:pharmacology*
chemical_list: D002147:Calmodulin; D012430:Ruthenium Red; D009219:Myosin-Light-Chain Kinase; D002118:Calcium