J. Biochem, 1990, Vol. 107, No. 6 872-878
© 1990 Japanese Biochemical Society
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Ca2+-Dependent Protein Phosphatase Which Dephosphorylates Regulatory Light Chain-a in Scallop Smooth Muscle Myosin1
Deparment of Chemistry, Faculty of Science, Hokkaido University Sapporo, Kita-ku, Hokkaido, Hokkaido 060
Ca2+-dependent protein phosphatase was purified from scallop adductor smooth muscle by a combination of DEAE-Toyopearl 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 at 1 µM free Ca2+ in the presence of calmodulin and 7 µM 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.
1 This study was aided by a Special Grant-in-Aid for Promotion of Education and Science in Hokkaido University provided by the Ministry of Education, Science and Culture of Japan.
2 Present address: Department of Biochemistry, Sapporo Medical College, South-1, West-17, Chuo-ku, Sapporo, Hokkaido 060.
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