Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Structural and functional changes in myosin of fast muscles during early post-natal development were studied to seek correlations with well-known physiological changes in the contraction rate. The findings were as follows: 1. It is known that fetal fast muscle myosin contains three kinds of light chains. It was confirmed that their molecular weights were the same as those of adult fast muscle myosin, but different from those of adult slow muscle myosin. The amount of the smallest light chain, g3, was confirmed to increase markedly during the postnatal period. 2. The ATPase [EC3.6.1.3] activity of fetal fast muscle myosin (-1 day) was found to be about 50% of that of adult myosin. The pH-activity curve of fetal myosin ATPase was confirmed to be similar to that of adult myosin. 3. The rate of formation of the reactive myosin-phosphate-ADP complex, MADPP, was found not to change during post-natal development. 4. It was found that the rate of decomposition of MADPP in the presence of F-actin increased markedly during the post-natal period, and that the rate of decomposition of the complex of fetal mysoin was only 1/6 to 1/4 of that of adult myosin. The change in the actomyosin ATPase activity was found to be closely correlated with the increase in the g3 content during development.
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PMID:Developmental changes in the structure and kinetic properties of myosin adenosinetriphosphatase of rabbit skeletal fast muscle. 0 17

The interaction of magnesium-ADP with skeletal muscle heavy meromyosin has been studied by measuring the accompanying release of protons. Total pH changes of the order of 0.03 were involved, and measurements were performed with a discrimination of some ten-thousandths of a pH unit. At pH 8.0 and 25 degrees C about 0.5 mol of protons per mol of heavy meromyosin is released at saturation. A stoichiometry of binding close to 2 mol of ADP per mol of protein was found, with a binding constant, obtained from the proton release titration curve (pH 8.0, 25 degrees C), of 2 X 10(5) M-1. At 5 degrees C the release of protons per mole is slightly greater, and the binding constant is somewhat increased, reflecting a negative enthalpy of binding. Similar proton release behavior is observed in the presence of manganous ions in place of magnesium. The liberation of protons is thus unrelated to the temperature-dependent isomerization of myosin in the presence of substrate. Alkylation of a reactive thiol group (SH1) does not change the proton liberation at pH 8.0. From the pH dependence of proton release, the association constant of heavy meromyosin with magnesium-ADP at other pH values can be inferred and shows an appreciable rise as the pH increases. The pH-proton release profile also allows the pK of the ionizing groups perturbed by the ligand to be deduced. At least two groups ionizing above pH 7 and one below are involved. Their pK's in the unperturbed state are assigned as 8.5, 9.3, and about 6.6, respectively; they are displaced in the complex to about 8.0, 9.1, and 6.3. A relation to the pH-activity profile of myosin ATPase is indicated. The pH-proton release profile is somewhat changed when the SH1 group is alkylated. Measurements with potassium-ADP, in the absence of magnesium, show that at pH 8.0 there is no proton release but rather a sizeable proton absorption (about 0.5 mol of protons per mol of heavy meromyosin). The association constant derived from the titration curves (pH 8.0, 25 degrees C) is 3 X 10(4) M-1.
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PMID:An investigation of heavy meromyosin-ADP binding equilibria by proton release measurements. 1 88

The effects of D2O on the elementary steps in the contractile and transport ATPase [EC 3.6.1.3] reactions were studied, and the following results were obtained: 1. The rate of H-meromyosin ATPase in the steady state decreased in D2O to 60% of that in H2O. Deuterium oxide did not affect the size or rate of the initial burst of Pi liberation, i.e. the amount or rate of formation of the reactive myosin-phosphate-ADP complex, MADPP. Moreover, neither the rate of change in the fluorescence spectrum of H-meromyosin induced by ATP (the rate of formation of the second enzyme-ATP complex, M2ATP) nor the rate constant of decomposition of MADPP into M degrees + ADP + Pi was affected by D2O. However, the equilibrium constant of the step M2ATP in equilibrium MADPP decreased in D2O to about 1/2 the value in H2O. 2. In the case of the Na+-K+-dependent ATPase reactin, neither the rate constant of formation of the second enzyme-ATP complex, E2ATP, nor that of decomposition of a phosphorylated intermediate, EADP approximately P, was affected by D2O. However, the equilibrium constant of the step E2ATP in equilibrium EADP approximately P decreased in D2O to about 1/2.5-1/4 of the value in H2O. These results suggest a similarity between the modes of binding of phosphate in MADPP in the myosin ATPase reaction and in EADP approximatley P in the Na+-K+-dependent ATPase reaction.
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PMID:Effects of deuterium oxide on elementary steps in the ATPase reaction. Evidence for the similarity of key intermediates in contractile and transport ATPase. 13 92

Bovine cardiac myosin ATPase activity was rapidly inactivated by the purine disulfide analog of ATP,6,6'-dithiobis(inosinyl imidodiphosphate). Kinetic investigations showed that this analog acted as a site-specific reagent at 0 degrees with a Ki of 130 muM and a half-life of 8.2 min at saturating inhibitor concentrations. Concentrations (50 to 500 muM) of ATP, adenyl-5'-yl imidodiphosphate (AMP-PNP), or ADP that saturated the active site caused an enhancement in the rate of inactivation, indicating the purine disulfide analog was not reacting at the active site. Under these conditions saturation kinetic data were still observed with Ki values remaining unchanged (120 muM) but with the half-life of inactivation decreasing to 6.0 min (ATP) and 4.6 min (AMP-PNP) at saturating inhibitor concentrations. At concentrations greater than 0.5 mM ATP, AMP-PNP, or ADP there was a decrease in the rate of inactivation, implying protection by these nucleotides. However, saturation kinetics of inactivation could no longer be demonstrated, implying a change in the mechanism of inactivation. A comparison of the inactivation of the Mg2+, Ca2+, and EDTA-ATPase activities of cardiac myosin after modification by the purine disulfide analog showed that the Mg2+- and Ca2+ATPase activities plateaued at approximately 60% and 40%, respectively, while the EDTA-ATPase activity continued to decrease to below 10%. This evidence supports the suggestion that the purine disulfide analog was not reacting at the active site. Equilibrium dialysis experiments were used to measure the binding of [8-3H]AMP-PNP to native cardiac myosin, the thiopurine nucleotide-modified myosin, and the derivative formed by displacing the thiopurine nucleotide by cyanide (thiocyanato-myosin). Native myosin bound a total of 2.1 mol of AMP-PNP with a binding constant of 6.0 X 10(6) M-1. There was a 15 to 40% decrease in the number of AMP-PNP binding sites in the enzyme derivatives, but the active sites appeared not to be blocked since the association constants remained essentially unchanged (KA=3.9 X 10(6) M-1 for thiopurine nucleotide-myosin and 12.0 X 10(6) M-1 for thiocyanato-myosin). The kinetic studies and the binding experiments indicate that the purine disulfide analog reacts at a specific site other than the active site but do not offer support to earlier suggestions from skeletal myosin studies that this site is a possible ATP control site.
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PMID:Reaction of cardiac myosin with a purine disulfide analog of adenosine triphosphate. I. Kinetics of inactivation and binding of adenylyl imidodiphosphate. 13 83

Kinetic measurement of the reaction of dynein ATPase (ATP phosphohydrolase, EC 3.6.1.3) extracted from the gills of Mytilus edulis shows that in the presence of Mg2+ there is a very rapid initial liberation of Pi from the dynein-ATP system, followed by a slower liberation in the steady state. In view of following results, we have confirmed that this phenomenon is not due to the accumulation of end products, a fall in substrate concentration, nor to the presence of labile impurities in ATP but is due to the catalytic activity of dynein ATPase. 1. The replacement of native dynein by heat denatured dynein or other kinds of Mg2+-ATPase could not produce such a burst phenomenon under the same condition. 2. Both the rate of initial burst and that of steady state were proportional to enzyme content over a wide range under our standard condition. 3. Initial burst was also observed under the constant ATP level by using a ATP generate system. 4. Preincubation of dynein with Pi prior to initiation of the reaction did not eliminate the initial burst. Some properties of the initial rapid liberation of dynein ATPase were also examined. These are shown below. 5. The free ADP liberation did not show any initial burst though the Pi liberation did in the initial phase and the rate of free ADP liberation was almost equal to that of Pi liberation of the steady state. 6. Mg2+ was more effective than Ca2+ for the appearance of the initial burst while the liberation of Pi in the steady state was activated more by Ca2+ than by Mg2+. The addition of K+ in the presence of Mg2+ resulted in a marked increase of Pi liberation in the steady state but not in the initial state. 7. The activation energy of the initial burst was 9.7 kcal, which is slightly smaller than that of myosin ATPase.
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PMID:Studies on the initial phase of dynein ATPase activity. 13 33

The Mg2+-dependent ATPase (adenosine 5'-triphosphatase) mechanism of myosin and subfragment 1 prepared from frog leg muscle was investigated by transient kinetic technique. The results show that in general terms the mechanism is similar to that of the rabbit skeletal-muscle myosin ATPase. During subfragment-1 ATPase activity at 0-5 degrees C pH 7.0 and I0.15, the predominant component of the steady-state intermediate is a subfragment-1-products complex (E.ADP.Pi). Binary subfragment-1-ATP (E.ATP) and subfragment-1-ADP (E.ADP) complexes are the other main components of the steady-state intermediate, the relative concentrations of the three components E.ATP, E.ADP.Pi and E.ADP being 5.5:92.5:2.0 respectively. The frog myosin ATPase mechanism is distinguished from that of the rabbit at 0-5 degrees C by the low steady-state concentrations of E.ATP and E.ADP relative to that of E.ADP.Pi and can be described by: E + ATP k' + 1 in equilibrium k' - 1 E.ATP k' + 2 in equilibrium k' - 2 E.ADP.Pi k' + 3 in equilibrium k' - 3 E.ADP + Pi k' + 4 in equilibrium k' - 4 E + ADP. In the above conditions successive forward rate constants have values: k' + 1, 1.1 X 10(5)M-1.S-1; k' + 2 greater than 5s-1; k' + 3, 0.011 s-1; k' + 4, 0.5 s-1; k'-1 is probably less than 0.006s-1. The observed second-order rate constants of the association of actin to subfragment 1 and of ATP-induced dissociation of the actin-subfragment-1 complex are 5.5 X 10(4) M-1.S-1 and 7.4 X 10(5) M-1.S-1 respectively at 2-5 degrees C and pH 7.0. The physiological implications of these results are discussed.
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PMID:Reaction mechanism of the magnesium ion-dependent adenosine triphosphatase of frog muscle myosin and subfragment 1. 14 77

Myosin was purified from the flight muscles of a flying (pigeon) and a nonflying (fowl) bird. Ki (ADP) of myosin ATPase of pigeon is higher, but the Km (ATP) is lower than that of fowl. The specific activity (mumole of Pi liberated/min/mg protein) is higher for the fowl. A0.5 (CaCl2) of myosin of both pigeon and fowl is similar. However, the two proteins differ in their interactions with ADP, ATP and p-chloromercuribenzoate. The two proteins have the same tyrosine, tryptophan and sulfhydryl contents. The electrophoretic patterns of the two myosins on SDS-polyacrylamide gels are different. These studies show significant molecular differences in the myosin derived from the flight muscles of a flying (pigeon) and a nonflying (fowl) bird.
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PMID:Comparative studies on myosin ATPase of a flying and nonflying bird. 15 58

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

A plasma-membrane fraction was isolated from a post-nuclear extract of human neutrophils by centrifugation through a linear sucrose density gradient. This fraction exhibited a Ca2+-dependent adenosine triphosphatase (ATPase) activity that could be differentiated from mitochondrial or myosin ATPase and from plasma-membrane Mg2+-dependent ATPase. When assayed in the presence of [gamma-32P]ATP, the Ca2+-dependent ATPase reaction resulted in the formation of an acid-resistant hydroxylamine-sensitive bond between the gamma-[32P] phosphate group and a membrane protein subunit with an apparent mol.wt. of 135000. Half-maximal activating effect of Ca2+ was found at 82nM and 0.18 microM for the ATPase and the formation of the 32P-membrane complex respectively. Generation of the phosphorylated product attained the steady state at 0 degrees C by about 30s, and was rapidly reversed by ADP. These results suggest that the Ca2+-activated ATPase reaction occurs through the formation of a phosphoprotein intermediate, similar to that described for some Ca2+-dependent ATPase enzymes associated with Ca2+ transport. The possibility thus exists that the neutrophil Ca2+-dependent ATPase catalyses a process of Ca2+ extrusion from the cell, thereby participating in the regulation of several Ca2+-dependent neutrophil functions.
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PMID:Calcium ion-dependent adenosine triphosphatase activity and plasma-membrane phosphorylation in the human neutrophil. 16 Feb 22

The kinetic parameters of the inhibition of monovalent cation activated myosin ATPase by ADP were investigated. The inhibitor constant (KI) was 1.65 X 10(-4) M and the maximal velocity (V) was 1.28 mumol Pi/mg myosin/min in the presence of 0.3M Kcl at 20 degrees C. The dependence of 1/VO on inhibitor concentration and the pH dependence of KI and Km (i.e. pKi approximately equal to pKm) show that the inhibition has a pure competitive character. The results are supported by energetic parameters, too. The enthalpy of the formation of (EI) complex was calculated. Similar results were obtained also in the presence of Rb+ activated myosin ATPase and subfragment-I K+ ATPase.
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PMID:Kinetic study of the inhibition of myosin ATPase activity by ADP. 16 61


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