Gene/Protein Disease Symptom Drug Enzyme Compound
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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)

Myocardial ischemia is characterized by a decrease in phosphocreatine (PCr) and Mg(2+)-ATP contents as well as an accumulation of myosin ATPase reaction products (inorganic phosphate [P(i)], protons, and Mg(2+)-ADP). The possibility that these metabolites play a role in rigor tension development was checked in rat ventricular Triton X-100-skinned fibers. Rigor tension was induced by stepwise decreasing [Mg(2+)-ATP] in the presence or in the absence of 12 mmol/L PCr. To mimic the diastolic ionic environment of the myofibrils, [free Ca2+] was set at 100 nmol/L (pCa 7); [free Mg2+], at 1 mmol/L; and ionic strength, at 160 mmol/L. In control conditions (pH 7.1, with no added P(i) or Mg(2+)-ADP), the pMg(2+)-ATP for half-maximal rigor tension (pMg(2+)-ATP50) was 5.07 +/- 0.03 in the presence of PCr. After withdrawal of PCr, the pMg2+)-ATP50 value was shifted toward higher Mg(2+)-ATP values (3.57 +/- 0.03). Addition of 20 mmol/L P(i) shifted the pMg(2+)-ATP50 to 3.71 +/- 0.04 (P < .05) in the absence of PCr and in the opposite direction to 4.98 +/- 0.02 (P < .01) in the presence of PCr. Acidic pH (6.6) strongly increased pMg(2+)-ATP50 in both the absence (3.90 +/- 0.03, P < .001) and presence (5.44 +/- 0.02, P < .001) of PCr. Conversely, Mg(2+)-ADP (250 mumol/L) decreased pMg(2+)-ATP50 to 3.26 +/- 0.06 (P < .001) in the absence of PCr; at pMg(2+)-ATP 4, no rigor tension was observed until PCr concentration was decreased to < 2 mmol/L. At acidic pH, maximal rigor tension was lower by 29% compared with control conditions, whereas in the presence of Mg(2+)-ADP, maximal rigor tension developed to 143% of the control value; P(i) had no effect. The tension-to-stiffness (measured by the quick length-change technique) ratio was lower in rigor (no PCr and pMg(2+)-ATP 6) than during Ca2+ activation in the presence of both PCr and ATP. Compared with control rigor conditions, this parameter was unchanged by Mg(2+)-ADP and decreased by acidic pH, suggesting a proton-induced decrease in the amount of force per crossbridge. In addition to their known effects on active tension, Mg(2+)-ADP and protons affect rigor tension and influence ischemic contracture development. It is concluded that ischemic contracture and increased myocardial stiffness may be mediated by a decreased PCr and local Mg(2+)-ADP accumulation. This emphasizes the importance of myofibrillar creatine kinase activity in preventing ischemic contracture.
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PMID:Myocardial ischemic contracture. Metabolites affect rigor tension development and stiffness. 815 39

Reactive oxygen species (ROS) have been reported to alter cardiac myofibrillar function as well as myofibrillar enzymes such as myosin ATPase and creatine kinase (CK). To understand their precise mode and site of action in myofibrils, the effects of the xanthine/xanthine oxidase (X/XO) system or of hydrogen peroxide (H2O2) have been studied in the presence and in the absence of phosphocreatine (PCr) in Triton X-100-treated cardiac fibers. We found that xanthine oxidase (XO), with or without xanthine, induced a decrease in maximal Ca(2+)-activated tension. We attributed this effect to the high contaminating proteolytic activity in commercial XO preparations, since it could be prevented a protease inhibitor, phenylmethylsulfonyl fluoride (PMSF), and it could be mimicked by trypsin. In further experiments, XO was pre-treated with 1 mmo1/L PMSF. Superoxide anion production by the X/XO system, characterized by electron paramagnetic resonance spin-trapping technique, was not altered by PMSF. A slight increase in maximal force was then observed either with X/XO (100 mumol/L per 30 mIU/mL) or H2O2. pMgATP-rigor tension relationships have been established in the presence and in the absence of PCr to separate the effects of ROS on myosin ATPase and myofibrillar-bound CK. In the absence of PCr, pMgATP50, the pMgATP necessary to induce half-maximal rigor tension, was reduced from 5.03 +/- 0.17 (n = 21) to 4.22 +/- 0.22 (n = 4) after 25 minutes of incubation in the presence one of 30 mIU/mL. XO and 100 mumol/L xanthine or to 4.04 +/- 0.1 (n = 11) after incubation in the presence of 2.5 mmol/L H2O2. The ROS effects were partially prevented or antagonized by 1 mmol/L dithiothreitol. No effect was observed on pMgATP50 when PCr was absent. pCa-tension relationships have been evaluated to assess the effects of ROS on active tension development. Incubations with H2O2 induced on increase in Ca2+ sensitivity and resting tension when MgATP was provided through myofibrillar CK (PCr and MgADP as substrates) but not when MgATP was added directly. These results suggest that myofibrillar CK was inhibited by ROS. Active stiffness and the time constant of tension changes after quick stretches applied to the fibers were dose-dependently increased by H2O2 only in the presence of PCr. In addition, myofibrillar CK but not myosin ATPase enzymatic activity was depressed after incubation with either ROS. These results suggest that ROS mainly alters CK in myofibrils, probably by the oxidation of its essential sulfhydryl groups. Such CK inactivation results in a decrease in the intramyofibrillar ATP-to-ADP ratio. The effects of ROS on cytosolic and bound CKs may take part in the overall process of myocardial stunning after cardiac ischemia and reperfusion.
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PMID:Creatine kinase is the main target of reactive oxygen species in cardiac myofibrils. 863 32

The purpose of this study was to examine the relationships between the relative contents of phosphocreatine (PCr), inorganic phosphate (Pi), beta-adenosine triphosphate (ATP), and transverse relaxation time (T2) with fiber composition, which determined histochemically in the human skeletal muscle. The vastus lateralis muscles of 28 volunteers were subjected to phosphorus nuclear magnetic resonance (31P NMR) spectroscopy, magnetic resonance imaging (MRI) and muscle biopsy. Muscle fibers were divided into type I and type II fibers using myosin ATPase stain. A wide range of fiber composition levels were observed in the subjects (27.3-74.6% type I fibers). The PCr/ATP, Pi/ATP and (PCr + Pi)/ATP ratios were positively related to the percentage of type II fibers (r = 0.695, p < 0.001, r = 0.429, p < 0.05 and r = 0.773, p < 0.001, respectively). There was no correlation between fiber composition and the PCr/Pi ratio (r 0.127, n.s.) or intracellular pH (r = 0.305, n.s.). Moreover, no correlation was found between T2 and fiber type (r = 0.144, n.s.). These results suggest that 31P NMR can detect the differences in relative content of phosphates between type I and type II fibers, thereby noninvasively evaluating fiber composition in human skeletal muscle.
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PMID:Relationships between fiber composition and NMR measurements in human skeletal muscle. 884 27

After discussing approaches to the modelling of mitochondrial regulation in muscle, we describe a model that takes account, in a simplified way, of some aspects of the metabolic and physical structure of the energy production/usage system. In this model, high-energy phosphates (ATP and phosphocreatine) and low energy metabolites (ADP and creatine) diffuse between the mitochondrion and the myofibrillar ATPase, and can be exchanged at any point by creatine kinase. Creatine kinase is not assumed to be at equilibrium, so explicit account can be taken of substantial changes in its activity of the sort that can now be achieved by transgenic technology in vivo. The ATPase rate is the input function. Oxidative ATP synthesis is controlled by juxtamitochondrial ADP concentration. To allow for possible functional 'coupling' between the components of creatine kinase associated with the mitochondrial adenine nucleotide translocase and the myofibrillar ATPase, we define parameters phi and psi that set the fraction of the total flux carried by ATP rather than phosphocreatine out of the mitochondrial unit and into the ATPase unit, respectively. This simplification is justified by a detailed analysis of the interplay between the mitochondrial outer membrane porin proteins, mitochondrial creatine kinase and the adenine nucleotide translocase. As both processes of possible 'coupling' are incorporated into the model as quantitative parameters, their effect on the energetics of the whole cell model can be explicitly assessed. The main findings are as follows: (1) At high creatine kinase activity, the hyperbolic relationship of oxidative ATP synthesis rate to spatially averaged ADP concentration at steady state implies also a near-linear relationship to creatine concentration, and a sigmoid relation to free energy of ATP hydrolysis. At high creatine kinase activity, the degree of functional coupling at either the mitochondrial or ATPase end has little effect on these relationships. However, lowering the creatine kinase activity raises the mean steady state ADP and creatine concentrations, and this is exaggerated when phi or psi is near unity (i.e. little coupling). (2) At high creatine kinase activity, the fraction of flow at steady state carried in the middle of the model by ATP is small, unaffected by the degree of functional coupling, but increases with ADP concentration and rate of ATP turnover. Lowering the creatine kinase activity raises this fraction, and this is exaggerated when psi or psi is near unity. (3) Both creatine and ADP concentrations show small gradients decreasing towards the mitochondrion (in the direction of their net flux), while ATP and phosphocreatine concentration show small gradients decreasing towards the myosin ATPase. Unless phi = psi = 0 (i.e. complete coupling), there is a gradient of net creatine kinase flux that results from the need to transform some of the 'adenine nucleotide flux' at the ends of the model into 'creatine flux' in the middle; the overall net flux is small, but only zero if phi = psi. A reduction in cytosolic creatine kinase activity decreases ADP concentration at the mitochondrial end and increases it at the ATPase end. (4) During work-jump transitions, spatial average responses exhibit exponential kinetics similar to those of models of mitochondrial control that assume equilibrium conditions for creatine kinase. (5) In response to a step increase in ATPase activity, concentration changes start at the ATPase end and propagate towards the mitochondrion, damped in time and space. This simplified model embodies many important features of muscle in vivo, and accommodates a range of current theories as special cases. We end by discussing its relationship to other approaches to mitochondrial regulation in muscle, and some possible extensions of the model.
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PMID:Theoretical modelling of some spatial and temporal aspects of the mitochondrion/creatine kinase/myofibril system in muscle. 974 25

The aim of this study was to evaluate myofibrillar creatine kinase (EC 2.7.3.2) activity on the background of the effect of substrate channeling by myosin ATPase and to compare it with creatine kinase (CK) activity of whole skinned fibers. In order to assess CK activity, skinned fibers were prepared from the rat psoas major muscles defined by light microscopy. The activity in permeabilized fibers after treatment with saponin, Triton X-100 and Ca(2+)-free medium reached 2.80, 6.97 and 3.32 micromol ATP min(-1) mg(-1) protein, respectively, when a coupled enzyme assay system with external hexokinase and glucose-6-phosphate dehydrogenase was used. Transmission electron microscopy (TEM) revealed a possible interference among activities of sarcolemmal, sarcoplasmic, myofibrillar and mitochondrial CK from persisting structures. For evaluation of the myofibrillar CK itself, a pure myofibrillar fraction was prepared. Fraction purity was confirmed by TEM and by enzymatic assays for marker enzymes. Two procedures, i.e. the coupled enzyme assay and the evaluation of phosphocreatine (PCr) concentration before and after the CK reaction, were used for measurement of CK activity in this fraction. The procedures resulted in 3.2 nmol ATP min(-1) mg(-1) protein and 7.6 nmol PCr min(-1) mg(-1) protein, respectively. These alternative approaches revealed a discrepancy between the reacting portions of PCr by more than 50 %, which provides information about the size of the effect, generally described as substrate channeling.
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PMID:Creatine kinase reaction in skinned rat psoas muscle fibers and their myofibrils. 1047 Aug 63

Several works have shown the importance of the creatine kinase (CK) system for cardiac energetics and Ca2+ homeostasis. Nevertheless, CK-deficient mice have cardiac function close to normal, at least under conditions of low or moderate workload. To characterize possible adaptive changes of the sarcoplasmic reticulum (SR) and potential role of glycolytic support in cardiac contractility we used the skinned fibre technique to study properties of the SR and myofibrils, in control and muscle-type homodimer (MM-/mitochondrial-CK)-deficient mice. In control fibres, SR Ca2+ loading with ATP and phosphocreatine (solution PL) was significantly better than loading with ATP alone (solution AL), as determined by analysis of caffeine-induced tension transients. Loading in the presence of ATP and glycolytic intermediates (solution GL) was not significantly different from solution PL. These data indicate that Ca2+ uptake by the SR in situ depends on a local ATP:ADP ratio that is controlled by both CK and glycolytic enzymes. In CK-deficient mice, Ca2+ loading was impaired in solution PL due to the absence of CK. In solution GL, loading was significantly increased, such that calculated Ca2+ release parameters were normalized to those in control fibres in solution PL. In CK-deficient mice, fibre kinetic parameters of tension recovery were impaired after quick stretch in solution PL and were not improved in solution GL. These results show that in CK-deficient mice, at least under basal conditions, glycolysis can replace the CK system in fueling the SR Ca2+ ATPase, but not the myosin ATPase, and may in part explain the limited phenotypic alterations seen in the hearts of these mice.
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PMID:Glycolysis supports calcium uptake by the sarcoplasmic reticulum in skinned ventricular fibres of mice deficient in mitochondrial and cytosolic creatine kinase. 1088 44

Since it was suggested in our previous study that ATP newly synthesized from ADP and phosphocreatine (PCr) by creatine kinase had an important role in Ca2+-induced phasic contraction in alpha-toxin permeabilized smooth muscle of rat proximal colon, we studied the role of newly synthesized ATP on myosin ATPase activity, by assessing a rate of force development as an index of myosin ATPase activity. The alpha-toxin-permeabilized preparations were thiophosphorylated by treatment with ATPgammaS. After the thiophosphorylation, the contraction induced by ATP plus PCr in the absence of Ca2+ reached the maximum at 30 s. When PCr was omitted from the bathing solution, the initial rate of the contraction was significantly slower, while the level of myosin light chain thiophosphorylation remained unchanged. An inhibitor of creatine kinase slowed the initial contractile rate to a rate similar to that induced by ATP alone. ADPbetaS had no effect on ATP plus PCr-induced contraction, suggesting that accumulation of ADP does not affect the initial rate of the contraction. PCr alone did not contract the thiophosphorylated-preparations. However, in the presence of ADP, PCr induced contraction at the initial rate which was slower than that induced by ATP plus PCr. These results indicate that newly synthesized ATP together with preexisting ATP is utilized as a substrate for myosin ATPase.
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PMID:The site where newly synthesized ATP is necessary for tension development in alpha-toxin permeabilized preparations of rat proximal colon. 1271 56

It is generally believed that cross bridges account for >50% of the total ATP consumed by skeletal muscle during contraction. We investigated the effect of N-benzyl-p-toluene sulfonamide (BTS), an inhibitor of myosin ATPase, on muscle force production and energy metabolism under near-physiological conditions (50-Hz stimulation frequency at 30 degrees C results in 35% of maximal force). Extensor digitorum longus muscles from mice were isolated and stimulated to perform continuous isometric tetanic contractions. Metabolites of energy metabolism were analyzed with fluorometric techniques. ATP turnover was estimated from the changes in phosphocreatine (PCr), ATP, and lactate (-2DeltaATP - DeltaPCr + [1.5Deltalactate]). During contractions (2-10 s), BTS decreased force production to approximately 5% of control. Under these conditions, BTS inhibited ATP turnover by only 18-25%. ATP turnover decreased markedly and similarly with and without BTS as the duration of contraction progressed. In conclusion, cross bridges (i.e., actomyosin ATPase) account for only a small fraction (approximately 20%) of the ATP consumption during contraction in mouse fast-twitch skeletal muscle under near-physiological conditions, suggesting that ion pumping is the major energy-consuming process.
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PMID:Cross bridges account for only 20% of total ATP consumption during submaximal isometric contraction in mouse fast-twitch skeletal muscle. 1659 21

High-frequency stimulation of skeletal muscle has long been associated with ionic perturbations, resulting in the loss of membrane excitability, which may prevent action potential propagation and result in skeletal muscle fatigue. Associated with intense skeletal muscle contractions are large changes in muscle metabolites. However, the role of metabolites in the loss of muscle excitability is not clear. The metabolic state of isolated rat extensor digitorum longus muscles at 30 degrees C was manipulated by decreasing energy expenditure and thereby allowed investigation of the effects of energy conservation on skeletal muscle excitability. Muscle ATP utilization was reduced using a combination of the cross-bridge cycling blocker N-benzyl-p-toluene sulfonamide (BTS) and the SR Ca2+ release channel blocker Na-dantrolene, which reduce activity of the myosin ATPase and SR Ca2+-ATPase. Compared with control muscles, the resting metabolites ATP, phosphocreatine, creatine, and lactate, as well as the resting muscle excitability as measured by M-waves, were unaffected by treatment with BTS plus dantrolene. Following 20 or 30 s of continuous 60-Hz stimulation, BTS-plus-dantrolene-treated muscles showed a 25% lower ATP utilization compared with control muscles. Furthermore, the ability of muscles to maintain excitability during high-frequency stimulation was significantly improved in BTS-plus-dantrolene-treated muscles, indicating a strong link between metabolites, energetic state, and the excitability of the muscle.
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PMID:Energy conservation attenuates the loss of skeletal muscle excitability during intense contractions. 1709 Jul 54

The effect of myosin ATPase inhibitor, 2,3-butanedione monoxime (BDM; used in the range of concentrations 1.25-10.0 mM), on recovery of functions of isolated rat heart subjected to normothermic (37 degrees C) total ischemia for 35 min has been investigated. BDM perfusion was performed at a flow rate of 4 ml/min during 5 min before ischemia (BDM-I) or before 25-min reperfusion (BDM-R). Control hearts were perfused with Krebs solution at the same flow rate. The highest functional recovery of heart and coronary vessels was observed during infusion of 2.5 mM BDM before ischemia. At the end of reperfusion ATP and phosphocreatine (PCr) content in hearts of this group was significantly higher whereas the level of lactate was two times lower than in control; total creatine content (sigmaCr) did not differ from the initial level. Similar but less pronounced changes in the improvement of aerobic metabolism and maintenance of sigmaCr after reperfusion were also observed in the case of infusion of 2.5 mM BDM before reperfusion. They were consistent with reduced recovery of functions of heart and coronary flow compared with these parameters observed in the BDM-I group. 2.5 mM BDM caused almost 2-fold decrease in release of cardiac lactate dehydrogenase into myocardial perfusate in the BDM-I and BDM-R groups (compared with control); this suggests lower damage of cell membranes. These results suggest that improvement of energy supply of postischemic cardiomyocytes may be a key factor determining cardioprotector effectiveness of short-term administration of BDM before ischemia.
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PMID:[The effect of myosin ATPase inhibition on metabolic and functional recovery of isolated rat heart after global ischemia]. 2000 Jan 23


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