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

The effect of F-actin upon the binding of ADP to rabbit skeletal muscle myosin, heavy meromyosin, and subfragment 1 was studied by equilibrium dialysis, ultracentrifuge transport, and light scattering techniques. Both myosin and H-meromyosin (HMM) bind a maximum of approximately 1.6 mol of ADP/mol of protein, while S-1 binds approximately 0.9 mol of ADP/mol of protein. The affinity for ADP of all three preparations was similar at a given ionic strength (approximately 10(6) M-1 at 0.05 M KCl) and decreased with increasing ionic strength. Under conditions similar to those used for the measurement of ADP binding, the binding sites of myosin, HMM, and subfragment 1 (S-1) are saturated with actin at molar ratios of 2, 2, and 1 mol of actin monomer/mol of protein, respectively, as determined by light scattering, ultracentrifuge transport, and in the case of myosin by ATPase measurements. F-actin was found to inhibit ADP binding, but even at an actin concentration at least twice that required for saturation of myosin, HMM, or S-1, significant ADP binding remained. This ADP binding was inhibited by 10(-4) M pyrophosphate. The observations are consistent with the formation of an actomyosin-ADP complex in which actin and ADP are bound to myosin at distinct but interacting sites.
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PMID:Effect of F-actin upon the binding of ADP to myosin and its fragments. 12 42

The extent of actin polymerization has been studied for samples in which the bound nucleotide of the actin was ATP, ADP, or an analog of ATP that was not split (AMPPNP). The equilibrium constants for the addition of a monomer to a polymer end were determined from the concentration of monomer coexisting with the polymer. An analysis of these results concludes that the bound ATP on G-actin provides little energy to promote the polymerization of the actin. AMPPNP was incorporated into F-actin and the interaction of F-actin - AMPPNP with myosin was studied. F-actin - AMPPNP activated the ATPase of myosin to the same extent as did F-actin - ADP. However, the rate of superprecipitation was slower in the case of F-actin - AMPPNP than in the control.
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PMID:The bound nucleotide of actin. 12 84

The metal ion requirement of myosin-ADP binding was investigated by use of Mn2+. Mn2+ binds to two sets of noninteracting sites on myosin which are characterized by affinity constants of 10(6) and 10(3), M(-1) at 0.016 M KCl concentration. The maximum number of sites is 2 for the high affinity and 20-25 for the low affinity set. Binding of Mn2+ to the high affinity sites increases the affinity of ADP binding to myosin. F-actin inhibits ADP binding (Kiely, B., and Martonosi, A., Biochim. Biophys. Acta 172: 158-170 [1969]), but even at F-actin concentrations much higher than that required to saturate the actin binding sites of myosin or its proteolytic fragments, significant ADP binding remained. The actin insensitive portion of ADP binding was inhibited by 10(-4) M inorganic pyrophosphate or ATP. The results are discussed on the basis of a model in which actin and ADP bind to myosin at distinct but interacting sites.
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PMID:The binding of Mn2+ and ADP to myosin. 12 87

Asakura, Taniguchi and Oosawa [1]proposed that muscle actin polymer under sonic vibration is in a different state from that of the ordinary double stranded helical structure (F-actin), characterised by partially interrupted structures of F-actin, a state of "f-actin". In order to confirm different states for actin polymers [1, 2], physicochemical studies were made by measurements of viscosity, flow birefringence, electric birefringence, fluorescence, electron microscopy, quasielastic light scattering and ATP splitting. The following results were obtained. (1) F-actin polymers can undergo two processes of depolymerization upon treatment with urea and various salts as judged by measurements of flow birefringence and viscosity: one is a rapid process in a solution containing K+ or Ca2+ and urea; the other is a slow process following a brief rapid one in a solution containing Mg2+ and urea. (2) In the presence of Mg2+ and a suitable concentration of urea, F-actin (FMU-actin) appeared to exhibit different properties than ordinary F-actin; it had lower viscosity and lower flow birefringence and it had on the whole a more flexible polymer structure, also judging from experiments of quasielastic light scattering, electric birefringence. The different structure was confirmed directly be electron microscopic observation. The aromatic side chains of FMU-actin were also more mobile than those of F-actin judging from fluorescence measurements. The transformation between F-actin and FMU-actin was reversible. (3) The state of FMU-actin polymers was also characterized by ATP splitting; FMU-actin split about one mole of ATP into ADP and inorganic phosphate per mole of actin monomer at room temperature, where F-actin did not. A molar excess of Mg2+ with respect to actin monomer at room temperature, where F-actin did not. A molar excess of Mg2+ with respect to actin monomer is required for ATP splitting. F-actin in solutions containing K+ or Ca2+ and urea did not split ATP. FMU-actin activated on Mg-ATP-ase of myosin at nearly the same rate as that of F-actin. (4) We have postulated a flexible filament model (f-actin). The relationships between the structure of f-actin and its functional role for force generation during contraction are discussed.
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PMID:Diphasic transformations of F-actin. Effects of urea and MgCl2 on F-actin. 13 Sep 28

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

The initial burst of Pi liberation during the hydrolysis of Mn(II)-ATP by heavy meromyosin from rabbit psoas muscle was investigated. Below 10 degrees, the initial burst of Pi liberation was inhibited by the pre-addition of ADP without any change in the steady-state activity, but it was not inhibited above 10 degrees. The burst size was about one mole per mole of heavy meromyosin. The initial burst of Pi liberation in Mg-ATP hydrolysis at 8 degrees, however, was not inhibited by the pre-addition of ADP. These results, obtained with psoas muscle heavy meromyosin, were almost the same as those obtained with heavy meromyosin from rabbit leg and back muscles (Hozumi and Tawada (1975) Biochim. Biophys. Acta 376, 1-12) and, therefore, indicate that in Mn-ATP above 10 degrees there is at the burst site a predominant myosin -product complex generated by ATP hydrolysis. Similarly, below 10 degrees there is a myosin-product complex identical with the one generated by adding ADP (and Pi) to myosin.
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PMID:Temperature-dependent transitions of the myosin-product intermediate at 10 degrees during Mn(II)-ATP hydrolysis by myosin from rabbit psoas muscle. 13 32

Cardiac and skeletal muscle myosins have been treated by N-ethylmaleimide in presence or absence of Mg-ADP. The variations of Ca2+ and K+-ATPase activities and the incorporation of N-[14C]ethylmaleimide into the whole myosin molecule and into its separated subunits (heavy and light chains) have been measured with N-ethylmaleimide treatment for different lengths of time. The results reported here show the following: 1. The Ca2+-ATPase activity of cardiac myosin is activated by N-ethylmaleimide treatment to a lesser extent than that of skeletal myosin. 2. The K+-ATPase activity of both myosins is inhibited in the same quantitative way. 3. The cardiac light chain L1 contains one highly reactive thiol group which is absent from the skeletal light chains. 4. The labelling of three SH-groups localized in the heavy subunits of both myosins induced the same degree of inactivation. 5. The difference observed between the degree of inhibition of the Ca2+-ATPase activity for the two types of myosin with longer treatments appears to be due to differences in the reactivity of the fourth--SH group labelled on the heavy chains.
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PMID:A comparative study of reactive--SH groups of cardiac and skeletal muscle myosins. 13 24

Myosins from rabbit white and red skeletal, rabbit heart, fish skeletal and chicken gizzard muscles, as well as from human platelets were subjected to trinitrophenylation by trinitrobenzene sulfonate and alkylation by N-ethylmeleimide which affected their amino and thiol groups, respectively. The blocking of amino groups was carried out in the presence or in the absence of Mg-ADP and was followed both spectrophotometrically and enzymatically. Essential amino groups, whose modification throughly changes the enzymic characteristics of myosin, were found in heart and in all skeletal muscle myosins but were absent in myosins from chicken gizzard muscle and from human platelets. The reaction of these amino groups was highly retarded in the presence of Mg-ADP. Alkylation of thiols led to loss of the K+-activated ATPase (ATP phosphohydrolase, EC 3.6.1.3) in all myosins. However, the rate of loss of activity varied from one myosin to another and, for a given myosin, was affected by the presence of nucleotides and by the value of the ionic strength. The change in Ca(2+)-activated ATPase activity (ATP phosphohydrolase, EC 3.6.1.3) on alkylation was influenced by the presence of Mg - ADP during the reaction. In the absence of this nucleotide, the Ca(2+)-ATPase activity increased and reached a plateau as a consequence of modification. The extent of activation largely depended on the origin of the myosin. When alkylation was carried out in the presence of Mg-ADP, the Ca(2+)-ATPase activity as a function of time exhibited a maximum but the descending part of the curve was absent in myosins from heart and gizzard muscles.
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PMID:Comparative studies on amino and thiol groups in myosins from different sources. 13 75

The kinetics of the Mg2+-dependent ATPase (adenosine triphosphatase) activity of bovine cardiac myosin and its papain subfragment-1 were studied by using steady-state and pre-steady-state techniques, and results were compared with published values for the corresponding processes in the ATPase mechanism of rabbit skeletal-muscle myosin subfragment-1. The catalytic-centreactivity for cardiac subfragment-1 is 0.019s-1, which is less than one-third of that determined for the rabbit protein. The ATP-induced isomerization process, measured from enhancement of protein fluorescence on substrate binding, is similarly decreased in rate, as is also the isomerization process associated with ADP release. However, the equilibrium constant for ATP cleavage, measured by quenched-flow by using [gamma-32P]ATP, shows little difference in the two species. Other experiments were carried out to investigate the rate of association of actin with subfragment-1 by light-scattering changes and also the rate of dissociation of the complex by ATP. The dissociation rate increases with increasing substrate concentration, to a maximum at high ATP concentrations, with a rate constant of about 2000s-1. It appears that isomerization processes which may involve conformational changes have substantially lower rate constants for the cardiac proteins, whereas equilibrium constants for substrate binding and cleavage are not significantly different. These differences may be related to the functional properties of these myosins in their different muscle types. Kinetic heterogeneity has been detected in both steady-state and transient processes, and this is discussed in relation to the apparent chemical homogeneity of cardiac myosin.
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PMID:The magnesium-ion-dependent adenosine triphosphatase of bovine cardiac Myosin and its subfragment-1. 13 61

2,4-Dinitrophenol (DNP) was found to cause a "clearing response" of myosin B in a medium in which "superprecipitation" of myosin B would otherwise take place. The effect of actin concentration on Mg-ATPase [EC 3.6.1.3] of HMM was studied in the presence and absence of DNP. The results indicate that DNP causes an increase rather than a decrease in the affinity of HMM for actin, and that it causes a decrease only in the actin-activated portion of the Mg-ATPase activity. Using a light-scattering technique, it was shown that neither the ATP-induced dissociation of acto-HMM nor subsequent reassociation is significantly affected by the presence of DNP. As for the formation of the myosin-phosphate-ADP complex in the myosin-ATPase reaction, it was shown that formation of the reactive complex is not affected by DNP. It can thus be concluded that DNP inhibits the decomposition of the actomyosin-phosphate-ADP complex, which is thought to be coupled with superprecipitation.
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PMID:2,4-Dinitrophenol as a specific inhibitor of the breakdown of the actomyosin-phosphate-ADP complex. 13 36


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