title: Ca2(+)-dependent protein phosphatase which dephosphorylates regulatory light chain-a in scallop smooth muscle myosin.
abstract: Ca2(+)-dependent protein phosphatase was purified from scallop adductor smooth muscle by a combination of DEAE-Toyoperal 650S ion exchange chromatographies and gel filtration on Sephacryl S-300. The phosphatase consisted of two subunits having molecular weights of 60 and 19 kDa. Phosphorylated regulatory light chain-a (RLC-a) was dephosphorylated by this phosphatase both in free and bound states in myosin prepared from the opaque portion of scallop smooth muscle (opaque myosin). The dephosphorylation was activated by Ca2+. The half maximal activation was a 1 microM free Ca2+ in the presence of calmodulin and 7 microM free Ca2+ in the absence of calmodulin. Opaque myosin phosphorylated at the heavy chain was not dephosphorylated with this phosphatase. p-Nitrophenyl phosphate was dephosphorylated. In addition to Ca2+, the phosphatase activity for RLC-a was activated by Mn2+, while p-nitrophenylphosphatase activity was activated by Mg2+ more strongly than by Mn2+. The pH-activity curves showed a maximum at pH 7 in the presence of Mn2+, but at around pH 8 in the presence of Mg2+. This phosphatase is similar to phosphatase 2B or calcineurin. The possible regulatory function of this phosphatase in scallop catch muscle is discussed.
authors.affiliation: Department of Chemistry, Faculty of Science, Hokkaido University.
authors.forename: K
authors.initials: K
authors.lastname: Inoue
authors.forename: H
authors.initials: H
authors.lastname: Sohma
authors.forename: F
authors.initials: F
authors.lastname: Morita
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D008974:Mollusca / Q000201:enzymology*; D009130:Muscle, Smooth / Q000201:enzymology*; D043263:Myosin-Light-Chain Phosphatase; D009218:Myosins / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000302:isolation & purification* / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D010749:Phosphoprotein Phosphatases; D043263:Myosin-Light-Chain Phosphatase; D009218:Myosins; D002118:Calcium