Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.4.1 (myosin ATPase)
 1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Regulated actin, F-actin plus troponin-tropomyosin, activates the myosin ATPase in the presence but not in the absence of calcium. Ultracentrifugation has been used to examine the interaction of regulated actin with two proteolytic fragments of myosin, heavy meromyosin (HMM), a two-headed species, and subfragment 1 (S-1), a single head. In the presence of ATP, the association constant (Ka) for the binding of S-1 to regulated actin is approximately 1.5 X 10(4) M-1, whether or not calcium is present. This is true for S-1 with and without the Mr = 19,000 phosphorylatable light chain. These results confirm the observations of Chalovich et al. (Chalovich, J., Chock, P. B., and Eisenberg, E. (1981) J. Biol. Chem. 256, 575-578) and support their suggestion that the inhibition of the regulated actin-activated ATPase of S-1 by removal of calcium does not result from preventing S-1 binding. The binding of HMM to regulated actin in the presence of ATP, however, is calcium sensitive. Removal of calcium results in approximately a 4-fold decrease in Ka, from 1.1 X 10(4) M-1 to 2.5 X 10(3) M-1. The results with HMM are more easily reconciled with the low stiffness of relaxed muscle and suggest a functional difference between S-1 and HMM.
J Biol Chem 1981 Dec 25
PMID:Calcium-sensitive binding of heavy meromyosin to regulated actin in the presence of ATP. 645 6

The Ca2+-binding component of troponin (TnC) and its proteolytic fragments containing Ca2+-binding sites I-III (TH1) or sites III and IV (TR2C) have been labeled with the fluorescent probes dansylaziridine (DANZ) at methionine 25 or 5-(iodoacetamidoethyl)amino-naphthalene-1-sulfonic acid (AEDANS) at cysteine-98. These probes report binding of Ca2+ to the low and high affinity sites, respectively. Fluorescence changes as a function of [Ca2+] were measured for the free peptides, their complexes with troponin I + troponin T, and these complexes bound to actin-tropomyosin in the presence of Mg2+ and ATP with and without myosin. An apparent Hill coefficient of 1.0-1.1 has been obtained for the Ca2+-induced fluorescence changes in TnC, its fragments, and their ternary complexes regardless of the label used. When a ternary complex containing appropriately labeled TnC or its fragment is bound to the actin-tropomyosin complex, the Hill coefficient for the titration of the low affinity sites increases to 1.5-1.6 and further increases to greater than 2 in the presence of myosin. To interpret the apparent Hill coefficients, we used a model containing two binding sites and a single reporter of the conformational change. Hill coefficients between 1.0 and 1.2 can be obtained for the fluorescence change without true cooperativity in metal binding, depending on the mechanism of the fluorescence change; i.e. the contribution of the singly or doubly occupied species to the fluorescence change. A Hill coefficient between 1.2 and 2, however, always indicates cooperativity in binding independently of the mechanism. Thus, our finding that fluorescence titrations of Ca2+ binding to TnCDANZ bound to actin-tropomyosin exhibit a Hill coefficient of 1.5 in the absence of myosin and 2.4 in its presence indicates the existence of true positive cooperativity in metal binding to sites I and II. No cooperativity was observed for AEDANS-labeled complexes that reflect Ca2+-binding to the high affinity sites. Plots of the Ca2+ dependence of myosin ATPase activity activated by actin-tropomyosin in the presence of any of the troponin complexes used had apparent Hill coefficients of approximately 4. The higher value suggests cooperative interactions in the activation of ATPase beyond those involved in Ca2+-binding to the Ca2+-specific sites.
J Biol Chem 1983 Dec 10
PMID:Cooperative binding to the Ca2+-specific sites of troponin C in regulated actin and actomyosin. 664 69

The intestinal epithelial cell brush border (BB) is a useful model for nonmuscle cell motility. We studied regulation of BB motility by analyzing myosin phosphorylation and its association with the cytoskeleton. Our results demonstrate that myosin associates with the cytoskeleton only when it is dephosphorylated. Myosin light chain kinase substrates release myosin, phosphorylated and in the form of filaments, from the cytoskeleton. Although ITP and GTP serve as myosin ATPase substrates, they do not cause BB contraction, myosin release, or phosphorylation. Brush border contraction occurs with ATP or with a mixture of ITP and ATP gamma S. Therefore, phosphorylation regulates myosin association with the cytoskeleton, myosin is not bound at the actin-myosin binding site, and when phosphorylated, myosin forms filaments for movement.
Cell 1983 Dec
PMID:Phosphorylation controls brush border motility by regulating myosin structure and association with the cytoskeleton. 665 77

The chick wrist muscle ulnimetacarpalis dorsalis (umd) has two heads. Using myosin ATPase and acetylcholinesterase (ACh.E) staining it was shown that one of the heads is composed almost entirely of acid-stable muscle fibres with multiple end plates (slow muscle fibres) and the other of acid-labile fibres with single end plates (fast muscle fibres). The development of the muscle was traced from E7 (Stage 32-33) when it is a relatively homogeneous mass, to E18. The two heads of the muscle are first distinguishable, by ATPase staining, at E8 (Stage 33-34) prior to their cleaving. Both heads of the muscle are innervated by motoneurons positioned laterally in the lateral motor column in spinal segments 15 and 16. There is no observable difference in the positions of the motoneuron pools to the two heads. At E18 the motoneurons innervating the fast head tend to be slightly larger than those innervating the slow head.
J Embryol Exp Morphol 1983 Dec
PMID:Development and motor innervation of a distal pair of fast and slow wing muscles in the chick embryo. 666 33

Diabetes appears to cause a cardiomyopathy independent of atherosclerotic coronary artery disease and hypertension. Left ventricular papillary muscle function studies in rats made severely diabetic with streptozotocin have shown a slowing of relaxation and a depression of shortening velocity. However, the effects of insulin therapy on the myocardial mechanics of diabetic rats have not been studied. Therefore, rats diabetic for 6-10 weeks were treated with PZI insulin for 2, 6, 10, or 28 days and the mechanical performance of their left ventricular papillary muscles was compared to that of untreated diabetics and age-matched controls; cardiac contractile protein enzymatic activity was also measured. Neither 2 nor 6 days of therapy had any effects on the depressed cardiac muscle performance of diabetic animals, although plasma glucose concentration was restored to normal. By 10 days of therapy, recovery of mechanical performance was nearly complete, and by 28 days of therapy, complete reversal of the altered myocardial mechanics was observed. Crystalline insulin added to the bath (9 mU/ml) had no effect on myocardial mechanics in either diabetics or controls. A gradual recovery of actomyosin and myosin ATPase activity in the hearts of insulin-treated diabetic animals was also found, complementing the mechanical studies. In addition to demonstrating a gradual but complete reversibility of the abnormalities in papillary muscle function in diabetic rats (although control of hyperglycemia was less than ideal), this study confirms that this model of a cardiomyopathy is not a result of streptozotocin-induced cardiac toxicity. Additional data are provided indicating that depressed thyroid hormone levels in diabetic rats are not responsible for the mechanical changes observed.
Circ Res 1981 Dec
PMID:Reversibility of diabetic cardiomyopathy with insulin in rats. 703 May 13

Sheep aorta thin filaments were prepared by ultracentrifugation of an ATP-containing extract in the presence of different concentrations of ethanediol. Thin filaments prepared without ethanediol contained small quantities of tropomyosin (0.027 Tm:actin) and caldesmon (0.017 CD:actin) and activated the MgATPase of skeletal myosin independently of Ca2+. Ultracentrifugation in the presence of 10-20% ethanediol resulted in preparation of thin filaments with increased content of tropomyosin (0.17 Tm:actin) and caldesmon (0.04 CD:actin). These thin filaments possessed high Ca(2+)-sensitivity in activation of skeletal muscle myosin ATPase. Besides actin, tropomyosin and caldesmon, thin filaments contained gelsolin and filamin. Gelsolin content (0.007 gelsolin:actin) was independent of the presence of ethanediol. The filamin content decreased from 0.015 to 0.007 mol:mol actin when the ethanediol concentration was increased from 0 to 20%, and was negatively correlated with the Ca2+ sensitivity of thin filaments. In a reconstituted system, pure filamin or gelsolin affected caldesmon regulation of actomyosin ATPase. Gelsolin (0.01:actin) reduced the inhibition of actomyosin ATPase caused by caldesmon and increased the potency of Ca(2+)-calmodulin in reversing this inhibition. Filamin (0.007:actin) also decreased the inhibitory action of caldesmon on actin-activated myosin ATPase and also potentiated the reversal of this inhibition by calmodulin. We conclude that minor components of smooth muscle thin filaments (gelsolin and filamin) significantly modify caldesmon mediated regulation of actomyosin ATPase. We suggest a tropomyosin-mediated mechanism by which filamin or gelsolin could exert similar effects.
J Muscle Res Cell Motil 1994 Dec
PMID:Filamin and gelsolin influence Ca(2+)-sensitivity of smooth muscle thin filaments. 770 23

Before the application of skeletal muscle in a cardiac-assist device, a preconditioning procedure is required in order to overcome the easy fatigability of this muscle. We evaluated the effect of preconditioning muscles while keeping their collateral blood supply. In 15 male rabbits, a skeletal muscle ventricle (SMV) was constructed from silicone and pectoralis major muscle with minimal dissection. In six rabbits, the muscle was electrically preconditioned. The pressure generated by the SMV was measured under various conditions. Histochemical fiber grouping was performed using myosin ATPase staining. The pressure rose with preconditioning despite an increase in slow-twitch fibers. The cross-sectional area of both slow-twitch and fast-twitch fibers increased significantly. The rise in pressure is attributable to muscle hypertrophy. The use of muscles with minimal dissection may avoid or shorten the vascular delay because of a well maintained blood supply and nearly isometric preconditioning.
Thorac Cardiovasc Surg 1993 Dec
PMID:Force and histochemical changes in rabbit pectoral muscle induced by chronic electrical stimulation for use in cardiac assistance. 812 62

The increasing interest in the metal ion aluminum fluoride and beryllium fluoride complexes as phosphate analogs in the myosin ATPase reaction and in muscle fiber studies prompted the examination of their interactions with the regulatory system of troponin and tropomyosin. In this work, the effects of these metal ion analogs on the spectral properties of the Ca(2+)-binding subunit of troponin, troponin C (TnC), were examined. In contrast to beryllium fluoride which did not change the spectral properties of TnC, aluminum fluoride binding induced an increase in both the alpha-helicity and the tyrosine fluorescence of TnC and exposed a hydrophobic region on this protein for fluorescent probe binding. Aluminum fluoride also reduced the Ca2+ and/or Mg(2+)-induced changes on TnC. These results indicate a direct interaction of aluminum fluoride with TnC and merit consideration in designing muscle fiber experiments with this phosphate analog.
Biophys J 1993 Dec
PMID:Aluminum fluoride interactions with troponin C. 831 88

The myosin head consists of a globular motor or catalytic domain that contains both the catalytic and actin binding sites, and a neck region which consists of a 8.5 nm alpha-helix that emerges from the globular part of the heavy chain and is stabilized by the binding of the essential and regulatory light chains. High levels of M754, a recombinant polyhistidine-tagged catalytic domain-like fragment of myosin II, were produced in Dictyostelium discoideum and purified using a rapid extraction protocol and metal chelate chromatography. Approximately 1.2 mg of homogeneous, functional protein was obtained per gram of cells. Kinetic analysis of M754 showed that the recombinant protein still has all the typical properties of a myosin ATPase. However, the removal of the light chain domain does have a pronounced effect on enzymatic activity. Nucleotide on-rates are 7-16-fold slower for M754 than for a myosin head fragment that includes the neck region. In contrast, the rate of ATP binding and dissociating the actin-bound catalytic domain is 10-fold increased. Overall the results indicate that the truncation of the heavy chain affects the nucleotide binding site and the communication between the nucleotide and actin binding sites. Furthermore, it seems that the nucleotide site of M754 is not fully formed but binding to actin or ATP stabilizes the structure in general and the nucleotide binding site in particular.
Biochemistry 1995 Dec 12
PMID:Kinetic characterization of the catalytic domain of Dictyostelium discoideum myosin. 851 62

The smooth muscle tropomyosin isoforms beta and gamma were isolated in pure form and labeled with N-(1-pyrenyl)iodoacetamide (PIA) on the cysteine residues at either the N- or the C-terminal region (Cys-36 and Cys-190 of beta- and gamma-isoforms, respectively). The effect of caldesmon (CaD) on local conformational changes in different regions of the tropomyosin molecule was determined on the basis of changes in the excimer fluorescence (excited dimer of pyrene) formed in homodimers of tropomyosin isoforms. In the absence of actin, excimer fluorescence from the pyrene at Cys-190 of gamma-tropomyosin homodimer decreased in a simple manner on the addition of CaD, whereas the excimer from the Cys-36 of beta-tropomyosin homodimer exhibited a biphasic change, suggesting that additional weak binding sites exist near Cys-36. In the presence of actin, CaD-induced changes in the excimer fluorescence of pyrene-tropomyosin were observed only with Cys-36, and this change was associated with an inhibition of actin-activated myosin ATPase. A competition study with unlabeled tropomyosin isoforms indicated that the different excimer changes exhibited by beta- and gamma-tropomyosin in the presence of CaD were due to conformational changes in different regions of the tropomyosin molecule and not to differences in their affinities for CaD. Experiments with recombinant CaD mutants derived using the baculovirus expression system showed that the inhibition of tropomyosin potentiation of actomyosin ATPase by CaD requires the regions between residues 728-756 and 718-727 on the CaD molecule, although the latter region was sufficient for direct interaction with tropomyosin.
Biochemistry 1995 Dec 26
PMID:Inhibition of smooth muscle actomyosin ATPase by caldesmon is associated with caldesmon-induced conformational changes in tropomyosin bound to actin. 852 57


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>