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Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In 2 mM MgATP, 0.08 ionic strength and 1 mM free Mg++ cardiac myofibrils bound 3.5 nmoles Ca/mg protein at maximal ATPase activation. Significant amounts of Ca were also bound to cardiac myosin with these same conditions. By subtraction of this myosin-bound Ca we obtained an estimate of 4 moles Ca bound per mole of myofibrillar troponin at maximal ATPase. We found, however, that Ca activation of myofibrillar ATPase could be estimated assuming that only two of troponin's Ca-binding sites are engaged in regulation of crossbridge activity. Increases in MgMTP from 0.3 to 5.0 mM raised the free Ca, giving half-maximal isomteric tension or ATPase. Although part of this shift is most probably due to changes in the number of rigor (nucleotide-free) actin-myosin linkages, the rightward shift of the free Ca++-activation relation with increase in MgATP from 2 to 5 mM appears to be due to effects of active (nucleotide-containing) actin-myosin linkages.
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PMID:Calcium regulation of cardiac myofibrillar activation: effects of MgATP. 12 91

The results of this work have shown that the actin-induced increase of the presteadystate extraphosphate production is depressed in the case of the trinitrophenylated myosin A. At the same time the onset of superprecipitation is delayed and the rate of turbidity change of the trinitrophenylated synthetic actomyosins is depressed significanylt. The results of these experiments failed to demonstrate any correlation between the steadystate ATPase activity of myosin A or actomyosin enzyme and the onset and rate of the superpricipitation reactions. The results of this study seem to indicate that the time resolution of the instruments used to monitor the turbidity changes during the superprecipitation reaction may be an important factor in the proper evaluation of the experimental results.
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PMID:Effect of trinitrophenylation on the correlation between ATPase activity and superprecipitation of skeletal actomyosins. 12 6

A study in the enzymatic properties of muscle membranes established that sarcolemma of the rabbit skeletal muscles contains the Ca2+-ATPase system which does not require Mg2+ for manifestation of ions activity. By some kinetic properties it differs from ATPase of myosin. The complex Ca-ATP2+ is a substrate of Ca2+-ATPase. Ions of a series of bivalent metals inhibit the latter as well as the passive transport of Ca2+, that may evidence for a definite relation of Ca2+-ATPase with Ca+2 transport in skeletal muscles. Acetyl cholinesterase and AMP-aminohydrolase are strongly bound with the sarcolemma. The sarcolemma structural organization is shown to play a certain role in manifestation of their activity. On the basis of the data obtained when studying the activity in the ATPase systems and dynamics of formation and decay of the intermediate phosphorylated product in the microsomal fraction of cow and rabbit myometrium certain peculiarities are established for the active mechanisms of Ca2+ transport in smooth muscles. A problem is under discussion on the possible active participation of sarcolemma in regulation of Ca2+ concentration in the smooth muscle cells. Two ATPase systems, Mg2+-dependent and Mg2+-dependent Ca2+ activated are found in nuclei; the role of lipids of the skeletal muscles in manifestation of their activity is studied. AMP-amino hydrolase properties are characterized for different areas of the sarcoplasmatic reticulum membranes. The model of E-avitaminous muscular distrophy was used to show disturbances in the structure of sarcolemma and membranes of the sarcoplasmatic reticulum which are accompanied by changes in their ATPase and Ca2+-transporting properties.
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PMID:[Enzymatic properties in muscle membranes]. 12 74

Under certain conditions the specific ATPase activity of myosin of a given muscle can be altered. The cause of this alteration can only lie in the myosin molecule itself. To produce an enzymatic activity of myosin, an interaction between their light and heavy chains is necessary. However, the specific activity appears to be determined mainly by light chains. Hence, one ought also to look for a basis of the changed activity in changes of the subunits of myosin. There are strong indications that the alterations in specific activity are accompanied by changes in the relative stoichiometry of the essential light chains of the respective myosin preparation. They differ in their pattern of subunits. The specific activity of a given kind of myosin seems to be determined by the combination of their light chains. Thus, a close correlation exists between these two properties of myosin (ATPase activity and structure of its molecule). There are sufficient indications, that these two properties of myosin correlate also with the mechanical capabiltiy of the corresponding muscle. Particularly the results of cross innervation studies demonstrate a close correlation between these three properties in skeletal muscle. The single subunits of myosin are produced and degraded independently and at heterogenous rates. The synthetis of these subunits is significantly accelerated in response to work overload. Thus, it is quite likely that the individual chains are non-coordinately synthesized, giving rise to variations in the relationship of different molecule types of myosin with different specific ATPase activity. Hence, the control mechanism to synthesize the individual subunits could also be the regulative mechanism to produce a myosin of the specific ATPase activity appropriate to the activity pattern of tissue.
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PMID:Editorial: Subunits of myosin. Relations to ATPase activity and mechanical function of muscle. 12 46

G-actin has been nitrated with tetranitromethane in conditions that lead to the modification of one tyrosine residue. The reactive residue was found by earlier workers to be Tyr-69. The nitrated actin is conformationally similar to native G-actin, as judged by sedimentation velocity and circular dichroism analysis. A small proportion only is in the form of covalently linked dimers and trimers. The nitrated G-actin will polymerise to form filaments, indistinguishable in the electron microscope from those of native F-actin, but the polymerisation process is slower. Reduction of the nitrophenol group to the corresponding aminophenol leaves the properties of the protein in respect of polymerisation unchanged. When a dansyl group is introduced at the same point, however, the ability of the actin to polymerise is lost. The nitrated actin and its reduced counterpart will also bind heavy meromyosin, and the characteristic arrowhead formation of the bound molecules along the filaments can be seen in the electron microscope. Neither of the modified F-actins, however, significantly activates or inhibits the myosin ATPase activity. The fluorescence of nitrated actin is strongly quenched through the presence of the nitrophenol chromophore. In soluble complexes with heavy meromyosin the fluorescence is indistinguishable from the sum of the separate contributions of the two protein components. There is thus no measurable excitation transfer between any tryptophan residues on the myosin heads, such as that inferred to be present in the ATPase site, and the nitrotyrosine in position 69 of the actin sequence. Implications of this observation are considered in relation to the different interaction sites in myosin and in actin. The activation of heavy meromyosin ATPase by copolymers containing actin and nitroactin in different proportions has been measured, and is not proportional to the fraction of native actin. The results are consistent with the view that the function of actomyosin depends on the interaction of the myosin heads with more than one actin subunit.
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PMID:Effects of specific chemical modification of actin. 12 59

"Basic" and "gross" free energy levels are defined for the discrete states of a macromolecular biochemical kinetic system such as a free energy transducing enzyme (e.g., myosin or Na,K-ATPase). Basic free energy level differences are related to the first-order rate constants for transitions between states while gross free energy differences, along with the corresponding fluxes, determine the rate of entropy production in the system. In muscle contraction the analysis is complicated by the possibility of the system doing external mechanical work. The question of the sign of the flux or of the gross free energy level change in a given transition is examined for both single-cycle and multi-cycle models. More definite statements can be made in single-cycle cases. Some numerical examples are included. The more complicated cases are reserved for a subsequent paper.
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PMID:Free energy levels and entropy production associated with biochemical kinetic diagrams. 12 55

"Basic" and "gross" free energy levels of a macromolecule such as myosin or Na,K-ATPase, defined in a previous publication, are discussed here for two relatively complicated cases: a six-state kinetic diagram of the sort that could be used to describe the actin activation of myosin-ATPase in solution; and muscle contraction, where a similar kinetic diagram is needed for each value of a positional variable X.
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PMID:Free energy levels and entropy production in muscle contraction and in related solution systems. 12 56

Muscle samples were obtained from the gastrocnemius of 17 female and 23 male track athletes, 10 untrained women, and 11 untrained men. Portions of the specimen were analyzed for total phosphorylase, lactic dehydrogenase (LDH), and succinate dehydrogenase (SDH) activities. Sections of the muscle were stained for myosin adenosine triphosphatase, NADH2 tetrazolium reductase, and alpha-glycerophosphate dehydrogenase. Maximal oxygen uptake (VO2max) was measured on a treadmill for 23 of the volunteers (6 female athletes, 11 male athletes, 10 untrained women, and 6 untrained men). These measurements confirm earlier reports which suggest that the athlete's preference for strength, speed, and/or endurance events is in part a matter of genetic endowment. Aside from differences in fiber composition and enzymes among middle-distance runners, the only distinction between the sexes was the larger fiber areas of the male athletes. SDH activity was found to correlate 0.79 with VO2max, while muscle LDH appeared to be a function of muscle fiber composition. While sprint- and endurance-trained athletes are characterized by distinct fiber compositions and enzyme activities, participants in strength events (e.g., shot-put) have relatively low muscle enzyme activities and a variety of fiber compositions.
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PMID:Skeletal muscle enzymes and fiber composition in male and female track athletes. 12 49

A comparison is made between dynein [flagellar ATPase; EC 3.6.1.3], purified from sea urchin sperm flagella, and muscle myosin. The amino acid composition of dynein was found to be statistically different from that of myosin. The same was true of their tryptic fragments retaining ATPase activity, i.e., Fragment A of dynein and heavy meromyosin. At low ionic strength, no superprecipitation took place when ATP was added to a mixture of dynein and actin, and stimulation of the Mg2+-ATPase activity of dynein remained below 50% even when a one-hundred-fold excess of actin was present. No viscosity drop was caused by adding ATP to a solution containing dynein and actin. Anti-myosin antiserum did not react with dynein, while anti-Fragment A antiserum formed no precipit-n line against myosin. Furthermore, the amount of dynein that combined with F-actin was less than one-fifth of the amount of dynein that fully combined with microtubules. These results are consistent with the dissimilarity in enzymatic and other physiocochemical properties of these two proteins.
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PMID:Amino acid composition of dynein and comparison with myosin. 12 68

Solution of thrombosthenin, the contractile protein complex isolated from pig platelets, have been studied by analytical ultracentrifugation and zone sedimentation in sucrose density gradients. Freshly prepared thrombosthenin in 0.6 M KCl shows a prominent peak in the ultracentrifuge with S degrees 20w about 5.5 and higher molecular weight aggregates (greater than 100S) sedimenting quickly to the bottom of the cell. Short term storage of high ionic strength solutions of thrombosthenin induces actomyosin-like gel formation and these gels dissociate with ATP and Mg2+ ions into two components of S degrees 20w 8.0 and S degrees 20w50. The supernatant, after actomyosin gel removal, contains only the S degrees 20w5.5 protein. From results of Ca2+ ATPase activity measurements and SDS polyacrylamide gel electrophoretic mobilities of dissociated thrombosthenin separated into fractions in sucrose density gradients, it is concluded that the S degrees20w5.5 protein species is the myosin-like protein of thrombosthenin. The S degrees 20w8.0 protein is not fibrinogen but also has myosin-like properties and is believed to be myosin dimer. Species of higher S values seen in the presence of ATP and Mg2+ in the analytical ultracentrifuge and located in the higher density zones of the sucrose gradients all gave in SDS polyacrylamide gel electrophoresis a single band of molecular weight 46-47,000 daltons. These subunit proteins appear to be derived from a range of polymeric variants of the F-actin-like protein of the contractile complex. All these higher density F-actin-like proteins readily form superprecipitates and display syneresis when combined with rabbit skeletal muscle myosin or platelet myosin. They are also all capable of conferring upon these two myosins a Mg2+ activated ATPase activity. It is suggested that in thrombosthenin solutions a myosin monomer-dimer equilibrium state exists which can be directionally influenced by a number of factors. The coexistence in the solution of F-actin and Mg2+ ATP, for example, increases the propensity of the myosin-like protein to form the higher molecular weight aggregate. Such aggregation may be the initiating mechanism for the intracellular organization of the thick filaments of the actomyosin complex, preparatory to a contractile event.
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PMID:Platelet contractile proteins: separation and characterization of the actin and myosin-like components. 12 96


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