Gene/Protein Disease Symptom Drug Enzyme Compound
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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)

Human skeletal natural actomyosin contained actin, tropomyosin, troponin and myosin components as judged by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Purified human myosin contained at least three light chains having molecular weights (+/-2000) of 25 000, 18 000 and 15 000. Inhibitory and calcium binding components of troponin were identified in an actin-tropomyosin-troponin complex extracted from acetone-dried muscle powder at 37 degrees C. Activation of the Mg-ATPase activity of Ca2+-sensitive human natural or reconstituted actomyosin was half maximal at approximately 3.4 muM Ca2+ concentration (CaEGTA binding constant equals 4.4 - 10(5) at pH 6.8). Subfragment 1, isolated from the human heavy meromyosin by digestion with papain, appeared as a single peak after DEAE-cellulose chromatography. In the pH 6-9 range, the Ca2+-ATPase activity of the subfragment 1 was 1.8- and 4-fold higher that the original heavy meromyosin and myosin, respectively. The ATPase activities of human myosin and its fragments were 6-10 fold lower than those of corresponding proteins from rabbit fast skeletal muscle. Human myosin lost approximately 60% of the Ca2+-ATPase activity at pH 9 without a concomitant change in the number of distribution of its light chains. These findings indicate that human skeletal muscle myosin resembles other slow and fast mammalian muscles. Regulation of human skeletal actomyosin by Ca2+ is similar to that of rabbit fast or slow muscle.
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PMID:Myosin and actomyosin from human skeletal muscle. 13 73

Myosin B exhibiting Ca2+ sensitivity in superprecipitation and Mg-ATPase [EC 3.6.1.3] activity was extracted from tracheal smooth muscle. Repeated washing with 2mM KCl and 1 mM NaHCO3 resulted in the loss of these activities. However, on addition of native tropomyosin, the myosin B regained its original properties. Native tropomyosin is the regulatory system in this smooth muscle.
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PMID:Regulatory protein of bovine tracheal smooth muscle. 13 35

The calcium activation of the ATPase (ATP phosphohydrolase, EC 3.6.1.3) activity of cardiac actomyosin reconstituted from bovine cardiac myosin and a complex of actin-tropomyosin-troponin extracted from bovine cardiac muscle at 37 degrees C was studied and compared with similar proteins from rabbit fast skeletal muscle. The proteins of the actin complex were identified by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Half-maximal activation of the cardiac actomyosin was seen at a calcium concentration of 1.2 +/- 0.002 (S.E. of mean) muM. A hybridized reconstituted actomyosin made with cardiac myosin and the actin-tropomyosin-troponin complex extracted from rabbit skeletal muscle was also activated by calcium but the half-maximal value was shifted to 0.65 +/- 0.02 (S.E. of mean) muM Ca2+. Homologous rabbit skeletal actomyosin showed half-maximal activation at 0.90 +/- 0.01 (S.E. of mean) muM Ca2+ and the value for a hybridized actomyosin made with rabbit skeletal myosin and the actin-complex from cardiac muscle was found at 1.4 +/- 0.03 (S.E. of mean) muM Ca2+ concentration. Kinetic analysis of the Ca2+ activated ATPase activity of reconstituted bovine cardiac actomyosin indicated some degree of cooperativity with respect to calcium. Double reciprocal plots of reconstituted actomyosins made with bovine cardiac actin complex were curvilinear and significantly different than those of reconstituted actomyosins made with the rabbit fast skeletal actin complex. The Ca2+-dependent cooperativity was of a mixed type as determined from Hill plots for homologous reconstituted bovine cardiac and rabbit fast skeletal actomyosin. The results show that cooperative interactions in reconstituted actomyosins were greater when the actin-tropomyosin-troponin complex was derived from cardiac than skeletal muscle.
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PMID:Cooperative interactions between the contractile proteins of cardiac and skeletal muscle. 13 46

In vertebrate smooth muscle actomyosin and myofibrils a myosin light chain of molecular weight about 20,000 becomes phosphorylated at the same Ca2+ concentration as required to stimulate the actin-activated ATPase activity of myosin. Further, the degree of phosphorylation in the preparations as well as in various reconstituted actomyosins is proportional to their measured Ca2+ sensitivity. The phosphorylation process is very rapid and is essentially completed before the rise in ATPase activity. The enzyme responsible for the observed myosin phosphoylation is a specific myosin light chain kinase which is routinely co-purified with myosin. This kinase is normally present in actomyosin and its removal together with tropomyosin leads to a complete loss of the actin-activated ATPase activity. It is suggested that the Ca-dependent phosphorylation of the light chain via the light chain kinase represents the initial step in the activation of myosin that leads to contraction. Relaxation is probably effected by an as yet uncharacterised light chain phosphatase.
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PMID:Ca-linked phosphorylation of a light chain of vertebrate smooth-muscle myosin. 13 9

In the presence of the regulatory protein complex tropomyosin-troponin ATPase activity of vertebrate skeletal muscle actomyosin is either higher or lower than in the absence of tropomyosin-troponin. The actual behavior depends on ionic strength, Ca2+ concentration, ATP concentration (determining the amount of rigor complexes present), and the ratio between actin and myosin. This effect of the myosin-actin ratio implies that under certain conditions cooperativity in actin-myosin interaction can be seen.
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PMID:Regulation of actin-myosin interaction. 14 Jun 53

The binding of 125I-labeled muscle tropomyosin to Acanthamoeba and muscle actin was studied by ultracentrifugation and by the effect of tropomyosin on the actin-activated muscle heavy meromyosin ATPase activity. Binding of muscle tropomyosin to Acanthamoeba actin was much weaker than its binding to muscle actin. For example, at 5 mM MgCl2, 2 mM ATP, and 5 micronM actin, tropomyosin bound strongly to muscle actin but not detectably to Acanthamoeba actin. When the concentration of actin was raised from 5 micronM to 24 micronM in the presence of 80 mM KCl, the binding of tropomyosin to Acanthamoeba actin approached its binding to muscle actin. As with muscle actin, the addition of muscle heavy meromyosin in the absence of ATP induced binding of tropomyosin in Acanthamoeba actin under conditions were binding would otherwise not have occurred. The most striking difference between the interactions of muscle tropomyosin with the two actins, however, was that under conditions where tropomyosin was found to both actins, its stimulated the Acanthamoeba actin-activated heavy meromyosin ATPase but inhibited the muscle actin-activated heavy meromyosin ATPase.
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PMID:Interaction between Acanthamoeba actin and rabbit skeletal muscle tropomyosin. 14 Aug 71

alpha-Actinin isolated from dog muscle was used to incite antibodies in rabbits, Antibodies, purified by affinity chromatography on CNBr-Sepharose coupled with alpha-actinin and then ferritin-labeled were found to localize on the Z disc of muscle sarcomeres. Molecules of alpha-actinin as an adsorbed monolayer on the surface of polystyrene Lytron particles could bind muscle-actin and tropomyosin from solution. Both the ATPase activity and superprecipitation of an erythrocyte-actin and muscle-myosin hybrid actomyosin complex were altered by alpha-actinin, while tropomyosin diminished these alpha-actinin effects. The binding properties of alpha-actinin are consistent with those of an anchoring protein for microfilaments in nonmuscle cells.
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PMID:alpha-Actinin and tropomyosin interactions with a hybrid complex of erythrocyte-actin and muscle-myosin. 14 86

A troponin-like complex has been isolated from bovine brain cortex. This tropinin-like complex, with brain tropomyosin, confers Ca2+ sensitivity to the actin-activated myosin adenosinetriphosphatase (ATP phosphohydrolase, EC 3.6.1.3). That is, the Mg2+-stimulated ATPase activity generated by the interaction of purified muscle actin with muscle myosin is inhibited in the absence of Ca2+ but not in the presence of Ca2+ as a result of the addition of both brain tropomyosin and troponin-like complex. The troponin-like complex contains three components, one of which is similar in molecular weight to the troponin-T of skeletal actomyosin.
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PMID:Isolation of troponin-like complex from bovine brain cortex. 14 51

The Ca2+-ATPase activity of cardiac myosin is increased in thyrotoxic animals. However, the physiological significance of this observation is uncertain since, in living muscle, Mg-ATP is hydrolyzed by myosin under the stimulating influence of actin. In this study, we have compared the actin-activated ATPase activity of myosin from euthyroid (myosin-N) and thyrotoxic (myosin-T) rabbits and the derivatives of myosin-N and myosin-T formed by blocking the most rapidly reacting class of thiols (SH1) with N-ethylmaleimide (NEM). Also, we have studied the activity of these myosins in the presence of a complex of troponin and tropomyosin that confers calcium sensitivity on the system. Vmax for the actin-activated ATPase of myosin-T was about 168% greater than for myosin N. The apparent dissociation constant for actin, Kapp, for myosin-T was about 42% of the normal value. After NEM modification, Vmax and Kapp for NEM-modified myosin-T and myosin-N decreased, becoming essentially the same for both myosins. In the presence of troponin-tropomyosin complex, the actin-activated ATPase of myosin-T exhibited calcium sensitivity that could be reduced by thiol modification. These results suggest that the SH1 thiols or the region near these groups are important to the actin-activated ATPase of myosin-N and are essential to the increased activity of myosin-T. Also, they suggest that the changes in the enzymatic properties of myosin induced by thyroxine may be responsible for altering the contractile properties of the heart.
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PMID:Actin-activated adenosine triphosphatase activity of native and N-ethylmaleimide-modified cardiac myosin from normal and thyrotoxic rabbits. 14 52

The regulatory mechanism in the aortic actomyosin system was studied. Superprecipitation of desensitized aortic myosin B was not exhibited even in the presence of Ca2+, but was observable only in the presence of native tropomyosin and Ca2+. Reconstituted actomyosin composed of pure aortic myosin and pure skeletal actin did not show superprecipitation. Addition of aortic native tropomyosin and Ca2+ caused a marked superprecipitation. The ATPase of reconstituted actomyosin was enhanced three- or fourfold by aortic native tropomyosin and Ca2+. The extent of superprecipitation of aortic myosin B did not show a biphasic type of response to Mg-ATP concentration. Thus, aortic native tropomyosin induces a real activation of the myosin, actin, and ATP system in the presence of Ca2+, in contrast with the case of skeletal native tropomyosin, which induces the depression of skeletal myosin-actin-ATP interaction in the absence of Ca2+.
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PMID:Regulatory mechanism in arterial smooth muscle contraction. 14 28


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