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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Purified skeletal muscle myosin (EC 3.6.1.3) has been covalently bound to Sepharose 4B by the cyanogen bromide procedure. The resulting complex, Sepharose-Myosin, possesses adenosine triphosphatase activity and is relatively stable for long periods of time. Under optimal binding conditions, approximately 33% of the specific ATPase activity of the bound myosin is retained. Polyacrylamide gel electrophoresis of polypeptides released from denatured Sepharose-Myosin indicates that 85% of the myosin is attached to the agarose beads through the heavy chains and the remainder through the light chains, in agreement with predictions of binding and release based upon either the lysine contents or molecular weights of themyosin subunits. The adenosine triphosphatase of the immobilized myosin has been investigated under conditions of varying pH, ionic strength, and cation concentration. The ATPase profiles of immobilized myosin are quite similar to those for free myosin, however subtle differences are found. The Sepharose-Myosin ATPase is not as sensitive as myosin to alterations in salt concentration and the apparent KM is approximately two-fold higher than that of myosin. These differences are probably due to chemical modification in the region of the attachment site(s) to the agarose beads and hydration and diffusion limitations imposed by the polymeric agarose matrix.
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PMID:Preparation and characterization of an enzymatically active immobilized derivative of myosin. 0 72

Cardiac myosin obtained from atria had a higher Ca2+-activated ATPase activity than did cardiac myosin from ventricles in various species of animals and in humans. The increased specific activity of Ca2+-activated adenosine triphosphatase (ATPase) of atrial myosin appeared to correlate with the level of the activity of ventricular myosin ATPase in the animal, since the same order in ATPase activity, as observed in ventricular myosins from various animals, was noted in atrial myosins. The enzymatic properties of atrial myosin also were characterized by no activation by N-ethylmaleimide, low activating energy, and a lower rate of inactivation at alkaline pH compared with the same properties of ventricular myosin. These findings suggest a difference in the myosin molecule at or near the active site, involving some sulfhydryl groups, between the two types of cardiac myosin. The Mg2+-activated ATPase activity, both in the presence and absence of actin (which is thought to be closely related to the basic contraction mechanism), also was enhanced in atrial myosin. Thus, the ATPase activities of atrial and ventricular myosins were different with special reference to the reaction pathway involving calcium and magnesium ions and appear to account for the difference in the velocity of contraction between the atria and the ventricles.
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PMID:Cardiac atrial myosin adenosine triphosphatase of animals and humans: distinctive enzymatic properties compared with cardiac ventricular myosin. 3 14

Fluorescein-labeled heavy meromyosin subfragment-1 (F-S-1) has been purified by ion exchange chromatography and characterized in terms of its ability to bind specifically to actin. F-S-1 activates the Mg++-adenosine triphosphatase activity of rabbit skeletal muscle actin and decorates actin as shown by negative stains and thin sections of rabbit actin and rat embryo cell microfilament bundles, respectively. Binding of F-S-1 to cellular structures is prevented by pyrophosphate and by competition with excess unlabeled S-1. The F-S-1 is used in light microscope studies to determine the distribution of actin-containing structures in wnterphase and mitotic rat embryo and rat kangaroo cells. Interphase cells display the familiar pattern of fluorescent stress fibers. Chromosome-to-pole fibers are fluorescent in mitotic cells. The glycerol extraction procedures employed provide an opportunity to examine cells prepared in an identical manner by light and electron microscopy. The latter technique reveals that actin-like microfilaments are identifiable in spindles of glycerinated cells before and after addition of S-1 or HMM. In some cases, microfilaments appear to be closely associated with spindle microtubles. Comparison of the light and electron microscope results aids in the evaluation of the fluorescent myosin fragment technique and provides further evidence for possible structural and functional roles of actin in the mitotic apparatus.
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PMID:Myosin subfragment binding for the localization of actin-like microfilaments in cultured cells. A light and electron microscope study. 7 3

A myosin was isolated from the clonal rat glial cell strain C-6 and compared with rat skeletal muscle myosin. After cell extracts were subjected to gel filtration chromatography in the presence of KI and magnesium pyrophosphate the C-6 myosin was rapidly purified by a procedure similar to that used for skeletal muscle myosin. The C-6 myosin resembles muscle myosin both physically and enzymatically. It contains heavy chains of 200,000 daltons and two classes of light chains of 17,000 and 19,000 daltons in approximately equal molar ratios. This myosin forms bipolar thick filaments in 0.1 M KCl and binds reversibly to skeletal muscle F-actin, the binding being inhibited by MgATP. Skeletal muscle F-actin stimulates the C-6 myosin adenosine triphosphatase 2- to 3-fold in the presence of KCl and Mg2+. The action activation of muscle myosin ATPase at low ionic strength is 10-fold greater than that of C-6 myosin. Ca2+ and EDTA stimulated the ATPase activities of both enzymes. When assayed in the presence of 0.6 M KCl and 1 mM EDTA the skeletal muscle myocin ATPase demonstrates substrate saturation while the C-6 myosin enzyme activity is stimulated by ATP concentrations above 2.5 mM.
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PMID:Purification and characterization of myosin from the clonal rat glial cell strain C-6. 12 31

Intrafusal fibres from the rat soleus were investigated for representative histochemical profiles in sedentary animals and animals chronically exercised for 17 weeks on a treadmill. The pattern of myosin adenosine triphosphatase (ATPase) activity in the polar region revealed three intrafusal fibre types: (1) myosin ATPase-dark (MD) fibres, alkali- and acid-stabile; (2) myosin ATPase-light (ML) fibres, alkali- and acid-labile; and (3) myosin ATPase-reversible (MR) fibres, alkali-stabile and acid-labile. The three fibre types were correlated with the level of reduced NADH diaphorase activity, with MR, ML and MD fibres staining dark, moderate and light, respectively. In the equatorial region the morphological features of representative ML and MD fibres revealed that they were nuclear bag fibres, while representative MR fibres were identified as nuclear chain fibres. The MR fibres in the exercised animals had higher levels of myosin ATPase alkaline stability and acid lability than MR fibres in the sedentary animals, suggesting the MR fibre profiles are selectively influenced by chronic exercise. The mean cross-sectional area of MR fibres from the exercised animals was significantly less than the MR fibres from the sedentary animals. In contrast to the effect of endurance training on NADH diaphorase activity in extrafusal muscle fibres, there was evidence of less activity in the MD fibres of the exercised animals.
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PMID:Histochemical profiles of rat soleus intrafusal fibres after chronic exercise. 12 93

When ATP binds to myosin in the presence of Mg2+ there follows a rapid cleavage reaction to yield a myosin-product complex whose breakdown is rate-limiting in the overall adenosine triphosphatase reaction at 21 degrees and pH 8.0. Recent kinetic studies on this system have led to the proposal that the cleavage of ATP bound to myosin is reversible. This conclusion is based in part on the observation that when ATP is mixed with an excess of myosin active sites a small amount of tightly bound ATP exists whose life-time coincides with that of the myosin-product complex and implies these two species are in equilibrium during their decay. Previous oxygen exchange studies have shown that phosphate released as free product contains more than one oxygen atom from water. A rapid equilibration between myosin-bound ATP and a myosin-products complex can account for the extra water oxygen incorporation of the product phosphate. Such a model requires that the gamma-phosphoryl group of the bound ATP also exchanges its oxygen atoms with water. Results presented in this paper show that protein-bound ATP labeled in the three terminal oxygen atoms of the gamma-phosphoryl group with 18O exchanges about 75% of its label within 2 s of binding to the active site of myosin. This result provides chemical evidence for a model in which bound ATP undergoes a reversible reaction with water. Incomplete exchange may arise from kinetic and/or structural restraints on the mechanism and plausible models are discussed.
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PMID:Oxygen exchange in the gamma-phosphoryl group of protein-bound ATP during Mg2+-dependent adenosine triphosphatase activity of myosin. 12 49

A histochemical study, using myosin-adenosine triphosphatase activity at pH 9.4, was conducted in soleus and plantaris muscles of adult rats, after bilateral crushing of the sciatic nerve at the sciatic notch. The changes in fiber diameter and per cent composition of type I and type II fibers plus muscle weights were evaluated along the course of denervation-reinnervation curve at 1, 2, 3, 4 and 6 weeks postnerve crush. The study revealed that in the early denervation phase (up to 2 weeks postcrush) both the slow and fast muscles, soleus and plantaris, resepctively, atrophied similarly in muscle mass. Soleus increased in the number of type II fibers, which may be attributed to "disuse" effect. During the same period, the type I fibers of soleus atrophied as much or slightly more than the type II fibers; whereas the type II fibers of plantaris atrophied significantly more than the type I fibers, reflecting that the process of denervation, in its early stages, may affect the two fiber types differentially in the slow and fast muscles. It was deduced that the type I fibers of plantaris may be essentially different in the slow (soleus) and fast (plantaris) muscles under study. The onset of reinnervation, as determined by the increase in muscle weight and fiber diameter of the major fiber type, occurred in soleus and plantaris at 2 and 3 weeks postcrush, respectively, which confirms the earlier hypotheses that the slow muscles are reinnervated sooner than the fast muscles. It is suggested that the reinnervation of muscle after crush injury may be specific to the muscle type or its predominant fiber type.
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PMID:Denervation and reinnervation of fast and slow muscles. A histochemical study in rats. 12 9

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

Two types of canine cardiac myosins, from the free wall of the left ventricle and from the free wall of the right ventricle, were compared with canine skeletal muscle myosin from gastrocnemius. For K+ -activated myosin the Vmax values in mumoles of Pi/mg.min were: right ventricle, 0.57 +/- 0.02; left ventricle, 0.72 +/- 0.09; gastrocnemius, 0.92 +/- 0.04. For Ca++ -activated myosin the Vmax values were: right ventricle, 0.32 +/- 0.04; left ventricle, 0.42 +/- 0.03; gastrocnemius, 0.52 +/- 0.02; (p greater than 0.01 for all defferences). For all three types of tissues the Vmax values for NH4+ -activated myosin were the same (2.30 +/- 0.11). Corresponding to kinetic changes there were significant changes in the proportion and type of myosin subunits. In the two cardiac ventricles where heavy chains were immunologically identical, 81% of the total nitrogen of right ventricular myosin was present in the heavy chains whereas in left ventricular myosin 90% of the total nitrogen of myosin was present in the heavy chains. Quantifications were made on polyacrylamide gels were dye binding was directly related to nitrogen concentration for each of the myosin chains. In canine skeletal muscle gastrocnemius where the myosin heavy chains were immunologically nonidentical with those of cardiac myosin, 87% of the total nitrogen was present in the heavy chains. The data suggest that there are 2 moles of myosin light chains per mole of myosin heavy chains in right ventricular myosin where the adenosine triphosphatase (ATPase) activity is low and 1 mole of myosin light chains per mole of myosin heavy chains in left ventricula myosin where ATPase activity is elevated; for skeletal muscle myosin there were 1.5 moles of myosin light chains per mole of myosin heavy chains. Proportion of myosin light chain C1 to light chain C2 was the same in both left and right ventricular myosin. In skeletal muscle myosin the proportion of light chain C1 to light chain C2 was significantly different from that of cardiac tissue. It appears that the proportion of myosin light chain C1 to light chain C2 is directly related to the type of myosin heavy chain present since the immunologically identical heavy chains of cardiac tissue were immunologically nonidentical with those of skeletal muscle myosin.
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PMID:Comparative analyses of skeletal and cardiac myosins. 12 33

Using myosin, heavy meromyosin, and subfragment-1 the steady state rate of Mg-modified adenosine triphosphatase (Mg-ATPase) was determined over a range of substrate concentrations between 10(-8) M and 5 X 10(-3)M, at 0.5 M and 0.05 M KC1 (pH 7.4 at 20 degrees C). At the substrate concentrations below 10(-5) M, myosin Mg-ATPase was observed to show that two active sites interact, as suggested by the analysis of transient kinetic studies (Walz, F. G., Jr.: J. Theor. Biol. 41, 357-373 (1973)). The increase in the activity at Mg-ATP concentrations higher than 10(-4) M corresponds to the binding of Mg-ATP to myosin sites not responsible for the catalytic action. With heavy meromyosin and subfragment-1, the activity was best expressed by the Michaelis equation. With heavy meromyonsin, the activation at high ATP concentrations is detectable, though not as pronounced as with myosin, but not with subfragment-1.
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PMID:The effects of substrate concentration on the Mg-adenosine triphosphatase activity of myosin. 13 Jan 98


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