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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)

Inhibition of the myosin ATPase by vanadate ion (Vi) has been studied in 90 mM NaCl/5 mM MgCl2/20 mM Tris-HCl, pH 8.5, at 25 degrees C. Although the onset of inhibition during the assay is slow and dependent upon Vi concentration (kapp approximately 0.3 M-1 s-1), the final level of inhibition approaches 100%, provided the Vi concentration is in slight excess over the concentration of ATPase sites. Inhibition is not reversible by dialysis or the addition of reducing agents. The source of this irreversible inhibition consists of the formation of a stable, inactive complex with the composition M . ADP . Vi (where M represents a single myosin active site). The complex has been isolated, and its mechanism of formation from M, ADP, and Vi has been studied. Omission of ATP increases the rate of formation by about 35-fold (kapp approximately 11 M-1 s-1), yet this rate is still low in comparison with the rates of simple protein-ligand association reactions. This slowness is interpreted in terms of a rate-limited isomerization step that follows the association of M+, ADP, and Vi: M+ . ADP . Vi leads to M+. ADP . Vi (+ indicates the inactive product of the isomerization). The properties of M.ADP.Vi are compared with those of the ATPase intermediate M**.ADP . Pi, and the possible role of Vi as an analog of Pi is discussed.
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PMID:Inhibition of myosin ATPase by vanadate ion. 15 22

Myosin from chicken pectoralis muscle consists of isozymes that differ in their alkali light chains. It is possible to isolate alkali 1 (A1) and alkali 2 (A2) homodimers of native myosin by immunoadsorption methods, and to compare their steady-state kinetics as well as their assembly into synthetic filaments under a variety of ionic conditions. Bipolar filaments of the isozymes formed at low salt concentrations had a narrow length distribution and did not differ from controls made from unfractionated myosin. Chicken myosin also assembles into highly homogeneous minifilaments similar to those formed by rabbit myosin in a citrate/Tris buffer. Analytical ultracentrifugation and electron microscopy showed that A1-homodimer, A2-homodimer and unfractionated myosin assembled into 0.3 micron short, bipolar minifilaments, which were indistinguishable from one another in size and shape. The steady-state myosin ATPase activity of the two homodimeric isozymes was identical in K+(EDTA) and Ca2+ assay media. The actomyosin Mg2+ ATPase measured at 25 and 55 mM-KCl (pH 8.0) showed only minor differences in both Vmax and Kapp. Actomyosin activity was also determined for the more homogeneous minifilament preparations of the isozymes and these, as well, produced essentially indistinguishable kinetic parameters. Thus we find no evidence to support the hypothesis that a particular alkali light chain of myosin can affect either the structure of the filaments or the steady-state rate of ATP hydrolysis.
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PMID:Assembly and kinetic properties of myosin light chain isozymes from fast skeletal muscle. 622 5

High concentrations of Tris are effective in dissociating actin-containing complexes, such as the red cell membrane cytoskeleton. A preparative procedure for red cell actin is based on the dissociation of the membrane skeletal complex in a buffer containing 1 M Tris hydrochloride, followed by gel filtration chromatography in the same medium. The actin is recovered as the monomer and is fully native, as judged by its critical concentration of polymerization, inhibition of DNase I, stimulation of myosin ATPase, and the appearance in the electron microscope of filaments, both bare and decorated with heavy meromyosin, and of magnesium ion-induced paracrystals. The Tris solution causes rapid depolymerization of F-actin with no denaturation, and the solution of monomeric actin in this medium is stable for many weeks in the cold; concentrated Tris is more reliable than guanidinium chloride for the depolymerization of F-actin in the estimation of total actin concentration by the DNase I inhibition assay.
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PMID:Concentrated Tris solutions for the preparation, depolymerization, and assay of actin: application to erythroid actin. 776 94