Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.4.1 (myosin ATPase)
 1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ATP-induced difference UV-absorption spectrum of myosin isolated from the opaque portion of scallop smooth muscle (opaque myosin) was Ca2+-sensitive at 40 mM KCl and 1.5 M sucrose. On adding sucrose to 1.5 M, the turbidity of myosin decreased to 24% and the characteristic two forms of the difference spectrum, the ATP-form and ADP-form (Morita, F. (1967) J. Biol. Chem. 242, 4501-4506), were distinguishable. In the presence of Ca2+, the difference spectrum was the ATP-form first and then decayed into the ADP-form with the depletion of ATP. In the absence of Ca2+, however, only the ADP-form was observed. The ADP-form observed in the absence of Ca2+ returned to the ATP-form when the regulatory light chain-a (RLC-a), one of the regulatory light chains of opaque myosin, was phosphorylated. These results suggest that the main intermediate at the steady state of opaque myosin ATPase is converted depending on the concentration of Ca2+, from EPADP in the presence of Ca2+ to EADP in the absence of Ca2+. It changes to EPADP in the absence of Ca2+ on the phosphorylation of RLC-a. Consistent results were obtained by measuring the ATP-induced Trp-fluorescence increase of opaque myosin in the absence of sucrose. Since the opaque portion of scallop smooth muscle is known to be responsible for catch contraction (Ruegg, J.C. (1961) Proc. R. Soc. London Ser. B 154, 224-249), these findings lead us to suppose that the opaque myosin in vivo may stay in the E.ADP complex during the catch state. It changes to EPADP by the phosphorylation of RLC-a, which may terminate the catch state.
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PMID:The steady state intermediate of scallop smooth muscle myosin ATPase and effect of light chain phosphorylation. A molecular mechanism for catch contraction. 297 52

Regulatory light chain-a myosin kinase (aMK), which phosphorylates one of the myosin regulatory light chains, RLC-a, contained in the catch muscle of scallop, was also found to phosphorylate heavy chains of scallop myosin. After incubation of myosin isolated from the opaque portion of scallop smooth muscle (opaque myosin) with aMK in the presence of [gamma-32P]ATP, about 2 mol of 32P was incorporated per mol of the myosin. The radioactivity was mostly found in the heavy chain at 0.26 M KCl. The pH-activity curve and MgCl2 requirement for the heavy chain phosphorylation were similar to those for RLC-a phosphorylation. In contrast, the dependency of activity on KCl concentration was different from that for RLC-a. The heavy chain phosphorylation activity decreased with increase in KCl concentration up to 0.06 M, and then increased at concentrations over 0.06 M to a maximum at around 0.26 M KCl. This complicated profile probably reflects the solubility of myosin, and the phosphorylation site may be located in the rod portion insoluble at low KCl concentrations. Phosphorylation of heavy chain did not change the solubility of the opaque myosin molecule at all. The acto-opaque myosin ATPase activity in the presence of Ca2+ was found to be decreased to less than one-fourth by the heavy chain phosphorylation.
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PMID:Regulatory light chain-a myosin kinase (aMK) catalyzes phosphorylation of smooth muscle myosin heavy chains of scallop, Patinopecten yessoensis. 297 85

FHC (familial hypertrophic cardiomyopathy) is a heritable form of cardiac hypertrophy caused by mutations in genes encoding sarcomeric proteins. The present study focuses on the A13T mutation in the human ventricular myosin RLC (regulatory light chain) that is associated with a rare FHC variant defined by mid-ventricular obstruction and septal hypertrophy. We generated heart-specific Tg (transgenic) mice with ~10% of human A13T-RLC mutant replacing the endogenous mouse cardiac RLC. Histopathological examinations of longitudinal heart sections from Tg-A13T mice showed enlarged interventricular septa and profound fibrotic lesions compared with Tg-WT (wild-type), expressing the human ventricular RLC, or non-Tg mice. Functional studies revealed an abnormal A13T mutation-induced increase in isometric force production, no change in the force-pCa relationship and a decreased Vmax of the acto-myosin ATPase. In addition, a fluorescence-based assay showed a 3-fold lower binding affinity of the recombinant A13T mutant for the RLC-depleted porcine myosin compared with WT-RLC. These results suggest that the A13T mutation triggers a hypertrophic response through changes in cardiac sarcomere organization and myosin cross-bridge function leading to abnormal remodelling of the heart. The significant functional changes observed, despite a low level of A13T mutant incorporation into myofilaments, suggest a 'poison-peptide' mechanism of disease.
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PMID:Myosin regulatory light chain mutation found in hypertrophic cardiomyopathy patients increases isometric force production in transgenic mice. 2209 67