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Query: UNIPROT:Q8N5D0 (ADP)
 37,930 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Measurements of birefringence, ultraviolet dichorism and quasielastic light scattering were carried out on F-actin in solution and on the thin filaments of glycerinated myofibrils. The birefringence of the I-bands of myofibrils was of the same order of magnitude as that of F-actin or the F-actin-tropomyosin-troponin complex oriented in vitro at the same concentration. The ultraviolet dichroism spectrum of the I-bands was very similar to that of F-actin or the F-actin complex in vitro, which is due to orientation of bound ADP and tryptophan residues in F-actin. Quasielastic light scattering measurements, electronmicroscopic observations and the analyses of the electro-optic effect of the I-bands suggested approximately the same flexibility for F-actin in vitro and for the thin filaments in vivo. These optical measurements which were made under various conditions provide evidence for a conformational change induced by calcium ions in F-actin both in vivo and in vitro. This conformational change was found to be amplified by the interaction of F-actin with myosin. This is a brief review of our investigation on the dynamics of F-actin and the thin filament in vivo and in vitro by optical methods.
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PMID:Dynamic characteristics of F-actin and thin filaments in vivo and in vitro. 57 53

By means of spin labeled analogs of ATP we have shown that conformational changes in myosin molecule induced by variation of temperature take place in the region of the active centre. In case of Mg-ATP and unmodified myosin conformation of the active centre changes monotonously with the change in temperature but after the modification of S1 thiol groups by N-ethylmaleimide on the temperature dependence curve of rotational mobility of the spin label a discontinuous is observed at 14-16 degrees C. It is also observed in case of K+-EDTA-ATP, or Ca2+-ATP and unmodified myosin. It is shown that the chemical analogs of Mg2+-paramagnetic ion Mn2+ are directly connected with the myosin active centre in the presence of ATP(ADP), i. e. a triple complex enzyme-bivalent cation-substrate is formed.
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PMID:[Interaction of a spin-labeled analog of ATP with myosin]. 62 21

The time course of oxygen-18 exchange between [18O]Pi and normal water, catalyzed by myosin subfragment 1 in the presence of MgADP, was followed using the shift in 31P NMR caused by the presence of oxygen-18 bound to the phosphorus. Essentially all molecules of [18O]Pi that bind to the enzyme undergo complete exchange and are released as [16O4]Pi. Exchange probably occurs by formation of myosin.ATP from a myosin.ADP.Pi complex and is rapid relative to release of Pi from this complex. The kinetics of exchange give a value for the rate constant for binding Pi to myosin.ADP of 0.23 M-1 S-1 (pH 8.0, 22 degrees C). This value is consistent with exchange occurring by reversal of the ATP-ase reaction back to the myosin.ATP complex.
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PMID:Kinetics of oxygen-18 exchange between inorganic phosphate and water catalyzed by myosin subfragment 1, using the 18O shift in 31P NMR. 64 Oct 45

Exchangeability of actin-bound ADP and calcium in actomyosin at low ionic strength has been studied using F-actin labelled with [14C]ADP or 45Ca and measuring release of radioactivity into solution. Low-speed centrifugation, ultracentrifugation and ultrafiltration were used to separate protein from the medium. Comparison of the results obtained with these three separation procedures has revealed that the release of [14C]ADP and 45Ca into the medium in the presence of millimolar concentrations of MgATP is largely due to the release under these conditions of actin itself retaining its bound ADP and calcium. The real exchange of the bound nucleotide and calcium, even under the most favourable conditions, was in our experiments limited to about 20%. Detailed examination of the dependence of both the release of actin and the exchange of actin-bound ADP and calcium on the free divalent cations present, the kind and concentration of the added nucleotide, and temperature of incubation indicates that there is no correlation between the exchange and superprecipitation of actomyosin. The results presented support the view that the limited enhancement by myosin of the exchange of nucleotide and cation bound to actin under certain conditions results from accidental disruption of bonds between actin monomers due to a mechanical stress exerted on actin filaments upon their interaction with myosin filaments.
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PMID:Changes in the state of actin during superprecipitation of actomyosin. 80 72

The tension of single fibers isolated from glycerinated rabbit psoas muscle was measured at various temperatures using Mg-ATP or Mn-ATP as a substrate. The tension developed in Mn-ATP was 80-89% of that in Mg-ATP at 4 degrees-16 degrees, and both tensions decreased as the temperature was reduced. Myosin forms the myosin-product complex predominantly generated on admixture with ADP (and Pi) at the burst site during Mn(II)-ATP hydrolysis below 10 degrees, while it forms the myosin-product complex predominantly formed via ATP hydrolysis upon hydrolysis above 10 degrees, as it does during Mg-ATP hydrolysis (Hozumi & Tawada (1975) Biochim. Biophys. Acta 376, 1; Tawada & Yoshida (1975) J. Biochem. 78, 293; Yazawa & Morita (1973) J. Biochem. 74, 1107). Since the cycle time of cross-bridge attachment to and detachment from actin in muscle is about 1-10 sec and because the spontaneous decay time of the myosin-product complex into the myosin-product complex in the absence of actin is less than 1 sec, then if most of the cross-bridges are detached from actin as suggested by X-ray data, it can be inferred that most of the cross-bridges detached from actin may form the predominant myosin-product complex in Mn-ATP below 10 degrees. If this is so, the tension development in Mn-ATP below 10 degrees cannot be compatible with some muscle models which assume the formation of the myosin-product complex by the cross-bridges prior to combination with actin during contraction.
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PMID:Temperature-dependence of tension development by glycerinated muscle fibers of rabbit psoas in Mn (II)-ATP and Mg-ATP solutions. 82 48

Subfragment-1 prepared by chymotryptic digestion of myosin was applied to a column of Sepharose-adipic acid hydrazide-ATP in 1 mM EDTA, 10 mM Tris-HCL (PH 7.6), and 40 mM KCL. Ninety-nine per cent of subfragment-1 was adsorbed on the column in this medium. Fourty-three per cent of the applied protein was eluted with 6 mM ADP in the above buffer and then 52% was eluted with 1 mM EDTA, 10 mM Tris-HCL (pH 7.6), AND 0.7 M KCL. The former fraction contained g3 chain and the latter g1 chain. These fractions were apparently the same as the components, p2 and p1, respectively, isolated by ion-exchange chromatography using DEAE-cellulose (Yagi & Otani (1974) J. Biochem. 76, 365-373). No significant difference of ADP binding was found between the two fractions, both could bind about 0.5 mole per 10(5) g of protein. The preparation of the two subfragment-1 fractions is described.
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PMID:Separation of myosin subfragment-1 into fractions containing g1 chani and g2 chain by Sepharose-adipic acid hydrazide-ATP column chromatography. 95 34

We report measurements of the reactivity (degree of labeling, as mole of ligand per mole of protein, at constant exposure time) of the reactive thiol, "SH1", of a subfragment of myosin (S-1), and of Cys-10 of F-actin under various conditions, using N-iodo-[3H]acetyl-N-(1-sulfo-5-naphthyl)ethylenediamine, a fluorescent radioactive iodoacetamide analog. When either ADP or adenyloyl imidodiphosphate (simulating unhydrolyzed ATP) is bound to the enzymatic site of S-1, the reactivity of "SH1" is slightly enhanced, but when active ATPase is going on, reactivity is reduced by about a third, presumably due to the species, (S-1) ADP,Pi. The reactivity of Cys-10 alone is very low. When the complex, (S-1)-F-actin, is formed, the reactivity of SH1 is strongly decreased, and the reactivity of Cys-10 is strongly increased. The foregoing results explain our further observation (on glycerol-treated rabbit psoas fibers) that when fibers labeled in relaxation solution are compared with fibers labeled in rigor solution, myosin is more reactive and actin is less reactive, in the former case; alpha-actinin and C-protein are also less reactive in the former case.
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PMID:Reciprocal reactivities of specific thiols when actin binds to myosin. 106 Nov 33

Centrifuge transport, equilibrium dialysis, and electron paramagnetic resonance studies on the binding of Mn2+ to myosin revealed two sets of noninteracting binding sites which are characterized at low ionic strength (0.016 M KCl) by affinity constants of 10(6) M-1 (Class I) and 10(3) M-1 (Class II), respectively. At 0.6 M KCl concentration, the affinity of Mn2+ for both sets of sites is reduced. The maximum number of binding sites is 2 for the high affinity and 20 to 25 for the low affinity set. Other divalent metal ions displace Mn2+ from the high affinity sites in the following order of effectiveness: Ca greater than Mg = Zn = Co greater than Sr greater than Ni. The inhibitory effects of Mg2+ and Ca2+ upon the Mn2+ binding are competitive with inhibitor constants of 0.75 to 1 mM which is similar to that of the low affinity divalent metal ion binding sites. Exposure of myosin to 37 degrees partially inhibits Mn2+ binding to Class I parallel with inhibition of ATPase activity. The binding of Mn2+ to the high affinity binding sites is not significantly influenced by ADP or PPi, although Mn2+ increases the affinity of ADP binding to myosin at high ionic strength.
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PMID:The binding of divalent cations to myosin. 115 63

In order to investigate the behavior of the energy-converting system in the myocardium, an experimental in vitro model was developed which consisted of contractile protein (myosin B) and mitochondria (Mit) prepared from canine cardiac muscle. In this system, ATP produced in Mit from added ADP caused the superprecipitation of the myosin B (My-B). One hour after the onset of experimental myocaridal infarction in the dog, the superprecipitation was very low in the system if Mit prepared from the infarcted myocardium were used, regardless of the origin of the myosin B. The respiratory control index of Mit prepared from infarcted was lower than that from noninfarcted myocardium, but the ADP:O ratio in Mit from infarcted myocardium, was little deteriorated. The findings indicate that a transferring process of an energy source from Mit to myosin B was markedly impaired in the infarcted myocardium. They also throw light on the mechanism by which the myocardium ceases its contraction at an early stage of infarction.
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PMID:Energy metabolism in the infarcted cardiac muscle: the interaction of contractile protein and mitochondria. 122 28

The interaction of a series of bifunctional reagents with skeletal muscle myosin has been studied. In the di-imido ester series dimethylmalonimidate failed to generate any cross-linked species, whereas the adipic and higher analogues gave dimers of myosin heavy chains. Analysis of free amino groups after reaction with these reagents and with the reducible species dimethyldithiobis(propionimidate) showed that no more than two to three cross-links per molecule were introduced. By contrast, the bifunctional reducible acylating agent, dithiobis(succinimidylpropionate), reacted with annihilation of about 10% of the amino groups under mild conditions that precluded the formation of intermolecularly linked species. Digestion of the intramolecularly cross-linked myosin with papain, followed by analysis of the fragments by gel electrophoresis, revealed extensive cross-linking between the globular heads of the myosin molecules. The subfragment 1 dimers regenerated subfragment 1 on reduction, as shown by the electrophoretic mobility and amino acid analysis. The extent of cross-linking, and therefore presumably the average relative orientation or freedom of the two heads, was unaffected by the addition of ADP and calcium ions. The internally cross-linked myosin retains practically its full calcium-activated adenosine triphosphatase activity, but in contrast to native myosin is soluble even at very low ionic strength. Circular dichroism measurements show that the alpha helical conformation is undisturbed in cross-linked myosin, but the sedimentation coefficient is considerably higher than that of the native protein, possibly due to freezing of the heads in a "closed" configuration. The light chaiins are not cross-linked to the heavy chains, except under extreme conditions that leads to intermolecular cross-linking and inactivation. The presence of calcium ions protects dithiobisnitrobenzoate light chains against degradation by papain.
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PMID:Chemical cross-linking of myosin. Disposition of the globular heads. 126 47


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