title: Two kinds of myosin phosphatases with different enzymatic properties from fresh chicken gizzard smooth muscle. Purification and characterization.
abstract: Two kinds of myosin phosphatases were purified from fresh chicken gizzard smooth muscle. Alkaline phosphatase (CGP-a), which requires Mg2+, was most active at pH 8.6 with 2 to 4 mM Mg2+, and was essentially the same as the phosphatase we reported previously (J. Biochem. 99, 1027-1036 (1986]. On the other hand, neutral phosphatase (CGP-b), was most active at pH 7.5 with 0 to 2 mM Mg2+, and was similar to SMP-IV reported by Pato and Kerc (J. Biol. Chem. 260, 12359-12366 (1985]. Although both phosphatases showed similar Vm (4.8 to 13 mumol/mg/min) using phosphorylated myosin head as the substrate under optimal conditions, CGP-b had a smaller Km (3.7 to 6.7 microM) than CGP-a by about 4-fold. CGP-b showed a lower Vm (1.9 to 8.4 mumol/mg/min) for the isolated myosin light chain than myosin itself, while CGP-a showed rather higher Vm (17 to 32 mumol/mg/min). Although the activity of CGP-a decreased monotonically with increase of ionic strength, that of CGP-b increased slightly with increase in NaCl until 0.1 M and then decreased. Those results suggest that CGP-b may be the effective myosin phosphatase in vivo. The analysis by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate showed that both phosphatases were composed of a single polypeptide having a molecular weight of 37,000. The tetrameric structure was assumed for both phosphatases, because the molecular weight in the native state was estimated as 140,000 or 145,000 for CGP-a or CGP-b, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Chemistry, Faculty of Science, Hokkaido University.
authors.forename: M
authors.initials: M
authors.lastname: Yoshida
authors.forename: K
authors.initials: K
authors.lastname: Yagi
mesh_terms: D000818:Animals; D002384:Catalysis; D002645:Chickens; D005895:Gizzard, Avian / Q000201:enzymology*; D007527:Isoenzymes / Q000032:analysis / Q000302:isolation & purification*; D009130:Muscle, Smooth / Q000201:enzymology*; D043263:Myosin-Light-Chain Phosphatase; D010749:Phosphoprotein Phosphatases / Q000032:analysis / Q000302:isolation & purification*
chemical_list: D007527:Isoenzymes; D010749:Phosphoprotein Phosphatases; D043263:Myosin-Light-Chain Phosphatase