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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)

Muscle fibre composition and capillarity were evaluated in frozen sections stained for myosin ATPase of the soleus and the white area of the medial head of the gastrocnemius of rats made hyperthyroid by injections of triiodothyronine (300-400 micrograms/kg body weight, every other day) for 2, 3 and 4 weeks. O2 consumption of homogenates of these muscles in the presence of excess inorganic phosphate (Pi) and ADP with pyruvate and malate as substrates was also measured. Increased oxidative capacity was observed in the soleus homogenates of hyperthyroid animals after 2 weeks of treatment while no changes were observed in the oxidative capacity of the homogenates of the white area of the medial head of the gastrocnemius, even after 4 weeks of treatment. Hyperthyroid animals showed a greater capillarity than controls in both muscles. In the soleus this was evident after 2 weeks of treatment while in the white area of the medial head of the gastrocnemius, it was evident only after 4 weeks of treatment. Fibre composition was affected in the soleus after 4 weeks of treatment. In control animals two fibre types were present in the soleus: slow-twitch oxidative fibres (s.o. or type I fibres) with a high ATPase activity after acid pre-incubation and fast-twitch glycolytic oxidative fibres (f.o.g. or type IIa fibres) with a low ATPase activity after acid pre-incubation. In the soleus of the hyperthyroid animals, a third fibre type with intermediate ATPase activity after acid pre-incubation was also present. This most probably represents a change in the type of myosin being synthesized by some fibres. No changes in fibre composition were observed in the white area of medial head of the gastrocnemius which was made up of only fast-twitch glycolytic fibres (f.g. or type IIb fibres). The changes in oxidative capacity and capillarity in the soleus preceded and did not seem to be related to the changes in the type of myosin being synthesized. The increased capillarity found in the white area of the medial head of the gastrocnemius of the hyperthyroid animals, in the absence of an increase in the oxidative capacity, indicates that the latter is not the only factor that determines capillarity in skeletal muscle.
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PMID:The effect of hyperthyroidism on capillarity and oxidative capacity in rat soleus and gastrocnemius muscles. 622 77

Isometric contraction and relaxation of glycerinated rabbit psoas muscle fibers containing native creatine kinase (CK) and ATPase activities were studied. Energy for contraction and relaxation was provided either by ADP + creatine phosphate (CP) or ATP alone, and the effectiveness of these additions on rate and maximum force of contraction and relaxation were compared. In the presence of 250 microM ADP, physiological concentration of CP (10 mM) produced faster and stronger contraction and faster and more complete relaxation than equimolar or even higher concentrations of ATP. When contraction was initiated by addition of ADP to fibers preincubated with 10 mM CP, the apparent Km for ADP was 1.18 +/- 0.24 mM. If the fibers were preincubated with ADP and contraction initiated by addition of 10 mM CP, the apparent Km for ADP was more than an order of magnitude smaller (76.0 +/- 4 microM). The observed Km for ADP for contraction was about half the Km for CP in solution (151.5 microM). The apparent Km for CP for rate of contraction was 2.67 +/- .046 mM independent of sequence of addition of ADP. Since these experiments were done in the presence of P1,P5-diadenosine 5'-pentaphosphate, a powerful inhibitor of adenylate kinase, the role of this enzyme in the process was not significant. These observations support the idea of compartmentation of myofibrillar CK in close function with myosin ATPase as part of the phosphoryl creatine energy shuttle.
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PMID:Myofibrillar end of the creatine phosphate energy shuttle. 623 38

The ribose-modified chromophoric and fluorescent analog of ATP 2',3'-O-(2,4,6-trinitrocyclohexadienylidene) adenosine 5'-triphosphate (TNP-ATP) has been synthesized previously (Hiratsuka, T., and Uchida, K. (1973) Biochim. Biophys. Acta 320, 635-647 and Hiratsuka, T. (1976) Biochim. Biophys. Acta 453, 293-297). In the present study, four TNP-derivatives of ATP, ADP, AMP and adenosine were synthesized and compared for several chemical, spectral and enzymatic properties. Their visible absorption and fluorescent properties were found to be quite similar. Visible absorption and fluorescence spectra of TNP-derivatives were sensitive to solvent polarity. TNP-adenosine and TNP-AMP showed considerable substrate activities with adenosine deaminase and alkaline phosphatase, respectively. TNP-ATP proved to be an excellent substitute for ATP in adenylate kinase and myosin ATPase systems. The results indicate that these analogs are useful as chromophoric and fluorescent probes for hydrophobic regions in adenine nucleoside and nucleotide requiring enzymes.
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PMID:Biological activities and spectroscopic properties of chromophoric and fluorescent analogs of adenine nucleoside and nucleotides, 2',3'-O-(2,4,6-trinitrocyclohexadienylidene) adenosine derivatives. 629 7

The K+ activated ATPase activity of myosin subfragment-1 was measured under different conditions and enzyme kinetic parameters were calculated. The logarithm of Km varies linearly with ionic strength down to very low KCl concentrations, the logarithm of k2 vs. ionic strength, on the other hand, considerably deviates from linearity at low concentrations of KCl. ADP is a competitive inhibitor, like myosin ATPase, and with practically the same inhibitor constant. The energetical parameters of the decomposition (to products and enzyme) of the S-1--ATP complex are partically the same as those for myosin, the parameters of its formation, however, differ from the corresponding values for myosin: delta SI is considerably, delta HI significantly higher in the case of myosin. This may be the result of some kind of interaction of the two heads of myosin.
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PMID:A kinetic study of the K+ activated ATPase of myosin subfragment-1. 645 May 8

Actin-myosin subfragment-1 (SF-1) or actin-heavy meromyosin is dissociated by the binding of ADP and vanadate (Vi) under conditions such that ADP alone does not dissociate the complex. The association constant of the stable complex M.ADP.Vi, in which M indicates myosin [Goodno, C. C. (1979) Proc. Natl. Acad. Sci. USA 76, 2620-2624] with actin is smaller than the average association constant of the intermediate states of the actin-SF-1 ATPase cycle. Actin-SF-1 ATPase activity is 90% inhibited by ADP plus vanadate. The reaction of actin with M.ADP.Vi produces a slow release of ADP and vanadate and quantitative recovery of ATPase activity. The rate of dissociation of ligands was almost linear in actin concentration; consequently, the rate constant of dissociation could only be roughly estimated as 0.5-1 sec-1. The rate of dissociation of ADP and vanadate is thus increased by a factor of 10(5) compared to M.ADP.Vi. The rate of release of ligands by regulated actin (actin-tropomyosin-troponin) was reduced to 1/10th to 1/20th by removal of calcium ion. Therefore the M.ADP.Vi complex has the properties of a more stable analogue of the myosin-ADP-phosphate complex that is generated in the normal ATPase cycle. The activation of ligand release (ratio of rate of dissociation of ADP and vanadate from actomyosin relative to myosin) is much larger than the activation of myosin ATPase by actin, whereas the actual rates of the reactions are much slower.
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PMID:Inhibition of actomyosin ATPase by vanadate. 645 80

The reactivity of thiol groups in cardiac myosin obtained from porcine ventricles was compared with that in rabbit skeletal myosin. 1. The specific thiol group, S2, of cardiac myosin became reactive to N-ethylmaleimide (NEM) upon the addition of Mg2+-ATP or Mg2+-ADP, as in the case of skeletal myosin, although to a lesser degree. Enhancement of the reactivity of S2 resulting from cooperative interaction between F-actin and Mg2+-ATP, but not Mg2+-ADP, which was first found in skeletal myosin, was also observed in cardiac myosin. 2. The total number of 5,5'-dithiobis(2-nitrobenzoate) (DTNB)-reactive thiols decreased in the presence of Mg2+ADP and decreased further in the presence of Mg2+-ATP for both myosins, in contrast to the concomitant increase in the reactivity of S2. The decrement was smaller in cardiac myosin than in skeletal myosin. 3. The DTNB-reactive thiols were classified into three groups with respect to their reactivity. The third or most slowly reacting thiol group, was found to be remarkably susceptible to Ca2+ at physiological concentrations (10(-8)-10(-6) M) in the presence of Mg2+-ADP for cardiac myosin, but in striking contrast, in the presence and relatively long-lived intermediate of myosin ATPase, the structure of which is sensitive to Ca2+, may be different in cardiac and skeletal myosins.
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PMID:Actin-induced local conformational change in the myosin molecule. III. Reactivity of S2 thiol and DTNB-reactive thiols of porcine cardiac myosin. 689 37

In the presence of vanadate (Vi) and ADP, myosin ATPase forms a stable inactive complex (myosin.ADP.Vi) at the active site. To elucidate the nature of the inactive complex, we studied the effect of Vi plus ADP on the interaction of heavy meromyosin (HMM) with F-actin. 1) Viscosity measurements showed that the actin-HMM rigor complex was dissociated into actin and HMM by Vi and ADP (both 10(-3) M range). 2) When the HMM.ADP.Vi complex isolated by gel filtration was mixed with actin in the absence of free Vi, about 60% of the added HMM formed a complex with actin, and more than 70% of the HMM bound to actin released Vi and ADP. 3) When a mixture of the isolated HMM.ADP.Vi complex with actin was dialyzed against a buffer without free Vi and free ADP, only less than 10% of Vi and ADP, which were originally bound to the HMM, were retained in the dialysis tube after 4 days. In contrast, if actin was omitted, about 80% of Vi and ADP were retained. 4) These results indicate that the HMM.ADP-Vi complex is dissociated from actin, and that Vi and ADP originally trapped at the HMM active site can be almost completely released from the active site by actin if free (released) Vi and ADP are concomitantly removed.
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PMID:Dissociation of actomyosin by vanadate plus ADP, and decomposition of the myosin-ADP-vanadate complex by actin. 704 12

The heavy chains of Acanthamoeba myosins. IA, IB and II, turkey gizzard myosin, and rabbit skeletal muscle myosin subfragment-1 were specifically labeled by radioactive ATP, ADP, and UTP, each of which is a substrate or product of myosin ATPase activity, when irradiated with UV light at 0 degrees C. With UTP, as much as 0.45 mol/mol of Acanthamoeba myosin IA heavy chain and 1 mol/mol of turkey gizzard myosin heavy chain was incorporated. Evidence that the ligands were associated with the catalytic site included the observations that reaction occurred only with nucleotides that are substrates or products of the ATPase activity; that the reaction was blocked by pyrophosphate which is an inhibitor of the ATPase activity; that ATP was bound as ADP; and that label was probably restricted to a single peptide following limited subtilisin proteolysis of labeled Acanthamoeba myosin IA heavy chain and extensive cleavage with CNBr and trypsin of labeled turkey gizzard myosin heavy chain.
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PMID:Direct photoaffinity labeling by nucleotides of the apparent catalytic site on the heavy chains of smooth muscle and Acanthamoeba myosins. 745 49

Electron paramagnetic resonance spectroscopy was used to monitor the orientation of muscle cross-bridges attached to actin in a low force and high stiffness state that may occur before force generation in the actomyosin cycle of interactions. 2,3-butanedione monoxime (BDM) has been shown to act as an uncompetitive inhibitor of the myosin ATPase that stabilizes a myosin.ADP.P(i) complex. Such a complex is thought to attach to actin at the beginning of the powerstroke. Addition of 25 mM BDM decreases tension by 90%, although stiffness remains high, 40-50% of control, showing that cross-bridges are attached to actin but generate little or no force. Active cross-bridge orientation was monitored via electron paramagnetic resonance spectroscopy of a maleimide spin probe rigidly attached to cys-707 (SH-1) on the myosin head. A new labeling procedure was used that showed improved specificity of labeling. In 25 mM BDM, the probes have an almost isotropic angular distribution, indicating that cross-bridges are highly disordered. We conclude that in the pre-powerstroke state stabilized by BDM, cross-bridges are attached to actin, generating little force, with a large portion of the catalytic domain of the myosin heads disordered.
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PMID:Muscle cross-bridges bound to actin are disordered in the presence of 2,3-butanedione monoxime. 761 40

We have used electron paramagnetic resonance (EPR) spectroscopy to detect ATP- and calcium-induced changes in the structure of spin-labeled myosin heads in glycerinated rabbit psoas muscle fibers in key physiological states. The probe was a nitroxide iodoacetamide derivative attached selectively to myosin SH1 (Cys 707), the conventional EPR spectra of which have been shown to resolve several conformational states of the myosin ATPase cycle, on the basis of nanosecond rotational motion within the protein. Spectra were acquired in rigor and during the steady-state phases of relaxation and isometric contraction. Spectral components corresponding to specific conformational states and biochemical intermediates were detected and assigned by reference to EPR spectra of trapped kinetic intermediates. In the absence of ATP, all of the myosin heads were rigidly attached to the thin filament, and only a single conformation was detected, in which there was no sub-microsecond probe motion. In relaxation, the EPR spectrum resolved two conformations of the myosin head that are distinct from rigor. These structural states were virtually identical to those observed previously for isolated myosin and were assigned to the populations of the M*.ATP and M**.ADP.Pi states. During isometric contraction, the EPR spectrum resolves the same two conformations observed in relaxation, plus a small fraction (20-30%) of heads in the oriented actin-bound conformation that is observed in rigor. This rigor-like component is a calcium-dependent, actin-bound state that may represent force-generating cross-bridges. As the spin label is located near the nucleotide-binding pocket in a region proposed to be pivotal for large-scale force-generating structural changes in myosin, we propose that the observed spectroscopic changes indicate directly the key steps in energy transduction in the molecular motor of contracting muscle.
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PMID:Resolution of three structural states of spin-labeled myosin in contracting muscle. 766 95


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