Modulatory effect of MgATP on smooth muscle myosin phosphatase activity

摘要: To deepen our understanding of the regulatory mechanism smooth muscle contraction, we examined properties myosin phosphatase (SMMP) which was purified from chicken gizzard according to method Alessi et al. with slight modifications. The SMMP a heterotrimer 130, 37 and 20 kDa subunits as reported. Because enzymatic activity strongly dependent on ionic strength, all experiments were carried out at constant strength 0.15 M. Vmax Km enzyme toward bovine stomach phosphorylated 25.2 μmol/mg protein/min 0.45 μM 25°C, respectively, implied that rate dephosphorylation by in cells should be comparable phosphorylation light chain kinase presence saturating Ca2+ concentration. ATP dose-de-pendently decreased one-fifth. IC50 for 0.6 uM 5 mM MgCl2, whereas it increased 10 absence Mg2+ addition 1 EDTA. ADP, AMP, GTP ITP showed no or only weak effect. finding ATPγS ineffective indicates 130 subunit cannot underlying mechanism. This modulation observed stomach, but not gizzard. difference conformation molecules MgATP may critical its modulatory