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Query: EC:3.6.4.1 (myosin ATPase)
 1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study was designed to investigate the changes in cardiac contractile properties induced by triiodothyronine (T3) administration in adult rats. Myofibrils and myosin were isolated from ventricular muscles from euthyroid and hyperthyroid animals and enzymatically and electrophoretically characterized. The time course of the isometric response, the force velocity curve, the force interval relation were studied in papillary muscles isolated from the right ventricles of euthyroid and hyperthyroid rats. T3 administration induced significant increases in Mg2+ activated myofibrillar ATPase activity (+11.4%) and in Ca2+ activated myosin ATPase activity (+20.1%). Significant increases in shortening velocity at low and zero loads (+20.4%) were found in papillary muscles from treated animals when compared with the control muscles. These variations in enzymatic activity and shortening velocity could be related to the increase in the amount of the fast isomyosin V1, as shown by pyrophosphate gel electrophoresis. The negative force-frequency relation at steady state, typical of rat cardiac preparations, was observed in treated and control animals; its slope was, however, halved in hyperthyroid papillary muscles when compared with control ones. In accordance with this finding, the potentiating effect of a prolonged diastolic interval was significantly reduced in hyperthyroid papillary muscles. In the frame of an interpretation of the force interval relation on the basis of the excitation contraction coupling processes, these latter observations might indicate an enhanced activity of the sarcoplasmic reticulum. We conclude that thyroid hormone administration has a dual effect on cardiac contractility, on one hand regulating the synthesis of the different isomyosin and, on the other hand, stimulating the activity of the sarcoplasmic reticulum.
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PMID:The dual effect of thyroid hormones on contractile properties of rat myocardium. 297 Jun 23

Hearts of genetically myopathic male hamsters (BIO 53 : 58) were studied at 1 month, 2 months, 3 months, 4 to 5 months and 7 months of age. The time course of alterations in the cardiac myofibrillar ATPase activity, the relationship of myofibrillar ATPase activity to free [Ca2+], myosin ATPase activity and the distribution of heavy chain myosin isoenzymes were evaluated. Mg2+-Ca2+ ATPase activity of cardiac myofibrils in myopathics was increased in 4 month and 7 month-old hamsters. Elevated Mg2+ ATPase activity was found as early as in 2-month-old hamster. However, there was no loss in the regulation of the myopathic myofibrillar assembly as measured by the PCa response (10(-7) M to 10(-4) M Ca2+). Scans of SDS electrophoresis slab gels of cardiac myofibrillar proteins from control (C) and myopathic animals (M) did not show any differences at any age group (1, 4 and 7 months). There was a significant decrease in myosin Ca2+ ATPase activity and actin activated Mg2+-ATPase activity at 4 to 5 months and 7 months of age in the myopathic hearts. At all ages in normal and myopathic animals cardiac myosin consisted of three isoenzymes, V1, V2 and V3. At all ages in controls and at 1 to 3 months in myopathics, V1 predominated and the isoenzyme distribution was V1 greater than V2 greater than V3. However, in myopathics at 4 to 5 months, the distribution was V1 = V3 greater than V2 and at 7 months was V3 greater than V2 greater than V1. Our experiments suggest alterations in different components of the contractile protein system that occur at different stages of myopathy.
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PMID:Multiple cardiac contractile protein abnormalities in myopathic Syrian hamsters (BIO 53 : 58). 315 46

Bovine aortic tropomyosin has been isolated by DEAE-Sepharose chromatography following isoelectric precipitation and ammonium sulfate fractionation. A single polypeptide [Mr 36 000 on a sodium dodecyl sulfate (SDS)-polyacrylamide gel] was obtained under different electrophoretic conditions. The amino acid composition of bovine tropomyosin was very similar to that of rabbit skeletal muscle; the amino-terminal residue is blocked. The molecular weight of the native tropomyosin (76 000), which is twice that calculated from the SDS-polyacrylamide gel, suggests that the molecule is a dimer. The diffusion coefficient of 3.4 X 10(-7) cm2 s-1 and the frictional coefficient of 1.7 indicate that the molecule is asymmetric. Comparative high-pressure liquid chromatography peptide mapping of rabbit skeletal and bovine aortic tropomyosins shows primary structure variation. Bovine aortic tropomyosin binds calcium under physiological conditions of pH and ionic strength (22 mol of Ca2+/mol of tropomyosin with a Kd of 1.4 mM). Such a property is not shared by skeletal tropomyosin. In low Mg2+ concentration, both skeletal and aortic actin activations of the skeletal myosin ATPase activity are calcium independent. Addition of aortic tropomyosin to a hybrid actomyosin (aortic actin, skeletal myosin) yields an enhancement of the actin activation of the myosin ATPase activity, but the addition of skeletal tropomyosin yields a decrease of this activity. However, both the enhancement and decrease are calcium dependent. Addition of skeletal or aortic tropomyosin to an actomyosin system, where both actin and myosin come from skeletal muscle, yields only an enhancement of the actin activation of the myosin ATPase activity.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Calcium binding of arterial tropomyosin: involvement in the thin filament regulation of smooth muscle. 407 89

The steady-state kinetics of the K+, Ca2+, and Mg2+-activated adenosine triphosphatase (ATPase) activities of rabbit skeletal myosin were investigated in the substrate concentration range from 0.05 microM to 5 mM and found not to follow Michaelis-Menten kinetics but rather to display biphasic behavior. The Ca2+-ATPase activity of myosin chymotryptic subfragment-1 (S-1), which has only one active site, also exhibits biphasic kinetics, thus excluding the possibility that the biphasic behavior is caused by negative cooperativity between the two active sites of myosin. Myosin K+ and Mg2+-ATPase are both activated by 5'-adenyl methylenediphosphonate (AdoPP[CH2]P) in a competitive manner at high substrate concentrations; i.e. the maximal velocity observed at high substrate concentrations is independent of the AdoPP[CH2]P concentration. This result provides evidence for substrate activation via binding to a regulatory site. Pyrophosphate inhibits myosin ATPase in a competitive manner at low substrate concentrations and in an uncompetitive manner at high substrate concentrations, with the uncompetitive Ki being smaller than the competitive Ki; i.e. pyrophosphate binds more tightly to the effector site than to the active site.
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PMID:Biphasic steady-state kinetics of myosin adenosine triphosphatase. Evidence for a substrate effector site. 610 32

Myosin purified from a murine myeloid leukaemia cell line (M1) that had been incubated with [32P]orthophosphate incorporated 32P into the heavy, but not the light, chain. When the heavy chain was dephosphorylated by bacterial alkaline phosphatase, myosin that had low actin-activated ATPase activity gained higher activity only in the presence of the light-chain kinase. In the absence of the light-chain kinase, however, the Mg2+-stimulated ATPase activity of myosin was not activated by actin, regardless of phosphatase treatment. These results indicate that the activity of M1 myosin ATPase is regulated by phosphorylation of both the light and heavy chains. A scheme for this regulation by phosphorylation is presented and discussed.
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PMID:Phosphorylation of the myosin heavy chain. Its effect on actin-activated Mg2+-stimulated ATPase in leukaemic myeloblasts. 613 30

Sarcolemmal Ca2+/Mg2+ ATPase was inhibited only about 30% by myosin antiserum that decreased myofibrillar ATPase activity by about 80%. There was a remarkable difference in the effect of myosin antiserum on sarcolemmal Ca2+/Mg2+ ATPase and myofibrillar ATPase with regard to its pre-incubation time with these organelles. Tryptic digestion of the sarcolemmal membrane did not show any change in its inhibitory effect of the myosin antiserum on Ca2+ ATPase. The data distinguish the Ca2+/Mg2+ ATPase from myosin ATPase and suggest that it is an enzyme of the sarcolemmal origin.
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PMID:Influence of myosin antiserum on heart sarcolemmal Ca2+ or Mg2+ ATPase activity. 614 77

To evaluate the combined effects of cardiac overload imposed by hypertension and by chronic exercise, male and female rats were made hypertensive by unilateral renal artery stenoses and made to exercise in an 8-10-wk swimming program. Sedentary normotensive animals, sedentary hypertensive animals and normotensive animals exposed to the swimming program were also studied. Hypertension was associated with the development of cardiac hypertrophy, and this was exaggerated in hypertensive swimmers. Actomyosin, Ca2+-myosin, and actin-activated Mg2+-myosin ATPase activities were enhanced in normotensive swimmers, depressed in hypertensives and were normal or increased in hypertensive swimmers. Myosin isoenzyme analysis showed a predominant V1 pattern in normals; an increase in percent V1 isoenzyme is swimmers; a predominant V3 pattern in hypertensives; and a return to the predominant V1 pattern in hypertensive swimmers. These findings suggest that the hypertrophy imposed by hypertension and hypertrophy imposed by physical training using a chronic swimming program are distinctly different biological phenomena. Physical training by swimming prevents the changes in cardiac myosin induced by hypertension despite the exaggeration of hypertrophy.
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PMID:Physiologic cardiac hypertrophy corrects contractile protein abnormalities associated with pathologic hypertrophy in rats. 621 15

Initial studies on molluscan muscle regulation indicated that thin filaments do not confer Ca2+-dependence on vertebrate myosin ATPase, and hence that molluscan muscles do not possess thin filament-linked regulatory systems. Subsequently it was shown that molluscan thin filaments do, in fact, impart Ca2+-sensitivity but only at Mg2+ concentrations greater than those used in the earlier studies. In the present study it is shown that Mg2+ prevents significant dissociation of tropomyosin and troponin subunits from thin filaments at the low monovalent ion concentrations typically employed to assay actomyosin ATPase; as a result Mg2+ allows expression of the molluscan thin filament regulatory system under these conditions.
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PMID:The ionic requirements for regulation by molluscan thin filaments. 622 62

A systematic study of the different fiber types of rat diaphragm muscle in the first 10 days after unilateral denervation showed approximately a 10% decrease in diameter of the white fibers, 25% increase in that of intermediate fibers, and 35% increase in that of red fibers together with diminished differential staining properties both for myosin ATPase and Sudan black. There was also a doubling of the amount of connective tissue. A reduction in total lipid concentration of the tissue included decreases in both triacylglycerol and phospholipid, but not cholesterol. Magnesium concentration in the tissue also declined, as did activity of Ca2+-activated, though not Mg2+-activated, myosin ATPase.
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PMID:Histochemical and biochemical characteristics of the transient hypertrophy of the denervated rat hemidiaphragm. 622 32

Myosin from chicken pectoralis muscle consists of isozymes that differ in their alkali light chains. It is possible to isolate alkali 1 (A1) and alkali 2 (A2) homodimers of native myosin by immunoadsorption methods, and to compare their steady-state kinetics as well as their assembly into synthetic filaments under a variety of ionic conditions. Bipolar filaments of the isozymes formed at low salt concentrations had a narrow length distribution and did not differ from controls made from unfractionated myosin. Chicken myosin also assembles into highly homogeneous minifilaments similar to those formed by rabbit myosin in a citrate/Tris buffer. Analytical ultracentrifugation and electron microscopy showed that A1-homodimer, A2-homodimer and unfractionated myosin assembled into 0.3 micron short, bipolar minifilaments, which were indistinguishable from one another in size and shape. The steady-state myosin ATPase activity of the two homodimeric isozymes was identical in K+(EDTA) and Ca2+ assay media. The actomyosin Mg2+ ATPase measured at 25 and 55 mM-KCl (pH 8.0) showed only minor differences in both Vmax and Kapp. Actomyosin activity was also determined for the more homogeneous minifilament preparations of the isozymes and these, as well, produced essentially indistinguishable kinetic parameters. Thus we find no evidence to support the hypothesis that a particular alkali light chain of myosin can affect either the structure of the filaments or the steady-state rate of ATP hydrolysis.
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PMID:Assembly and kinetic properties of myosin light chain isozymes from fast skeletal muscle. 622 5


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