title: Inhibitory Ca(2+)-regulation of myosin light chain kinase in the lower eukaryote, Physarum polycephalum: role of a Ca(2+)-dependent inhibitory factor.
abstract: ATP-dependent interactions between myosin and actin in the lower eukaryote, Physarum polycephalum, are inhibited by micromolar levels of Ca2+. This inhibition is mediated by the binding of Ca2+ to myosin, the phosphorylation of which is required if Ca2+ is to inhibit the activities of myosin (Kohama, K., Trends Pharmacol. Sci. 11, 433-435 (1990)). As the first step to examine whether Ca2+ also regulates phosphorylation in the actomyosin system, we purified myosin light chain kinase (MLCK) of 55 kDa almost to homogeneity. The MLCK activity was high whether or not Ca2+ was present. However, a Ca(2+)-dependent inhibitory factor (CIF) purified from Physarum (Okagaki et al., Biochem. Biophys. Res. Commun. 176, 564-570 (1991)) was shown to reduce the MLCK activity in a Ca(2+)-dependent manner. Using crude preparations, not only MLCK but also myosin heavy chain kinase and actin kinase were shown to be inhibited by Ca2+ half-maximally at micromolar levels. Since CIF is the only Ca(2+)-binding protein in the preparations, we propose that this inhibitory Ca(2+)-regulation of the kinases for actomyosin is mediated by CIF.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, University of Tokyo, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Okagaki
authors.forename: R
authors.initials: R
authors.lastname: Ishikawa
authors.forename: K
authors.initials: K
authors.lastname: Kohama
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism; D002227:Carbazoles / Q000494:pharmacology; D004789:Enzyme Activation; D026121:Indole Alkaloids; D007211:Indoles; D008954:Models, Biological; D009219:Myosin-Light-Chain Kinase / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D010770:Phosphotransferases / Q000187:drug effects / Q000378:metabolism; D016839:Physarum polycephalum / Q000187:drug effects / Q000378:metabolism*; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D015800:Protozoan Proteins; D013050:Spectrometry, Fluorescence
chemical_list: D002147:Calmodulin; D002227:Carbazoles; D026121:Indole Alkaloids; D007211:Indoles; D047428:Protein Kinase Inhibitors; D015800:Protozoan Proteins; C059549:NA 0344; C059550:NA 0345; C049985:staurosporine aglycone; D010770:Phosphotransferases; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D009219:Myosin-Light-Chain Kinase; C033142:myosin-heavy-chain kinase; D002118:Calcium