Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

The kinetic influence of bound creatine kinase (CK) on the Ca(2+)-activated myosin ATPase was evaluated. ATPase rates were measured from 0.8 microM to 3.2 mM MgATP. Under control conditions, the apparent KmATP was 79.9 +/- 13.3 microM. In contrast, the addition of 12.2 mM phosphocreatine (PCr) decreased the apparent KmATP to a value of 13.6 +/- 1.4 microM. To determine if this reduction was merely the result of an ATP maintenance system, ATP was regenerated using either phosphoenolpyruvate and pyruvate kinase (PEP-PK), or PCr and soluble bovine cardiac CK. Data obtained with PEP + PK indicated an apparent KmATP of 65.5 +/- 7.3 microM. To study the effects of exogenous CK, the endogenous CK was irreversibly inhibited with 1 mM iodoacetamide. The kinetics of the ATPase were then examined by adding soluble CK to the incubation medium. Under these conditions, the KmATP was 56.4 +/- 0.86 microM. Therefore, these two ATP regeneration systems could not duplicate the effects of endogenous CK. The reduction of the apparent KmATP by endogenous CK was not the result of an altered inhibition by MgADP. MgADP inhibition was determined to be non-competitive, with a Ki of 5.0 +/- 0.1 mM. These data suggest that the observed kinetic effects reflect the proximity of the enzymes in the myofibrillar bundle, thus emphasizing the importance of bound CK for the localized regeneration of MgATP utilized by the myosin ATPase.
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PMID:Specific enhancement of the cardiac myofibrillar ATPase by bound creatine kinase. 153 Nov 42

1. We tested the hypotheses that coupling between oxidative metabolism and force in noradrenaline (NOR)-activated rabbit aorta is controlled (a) by an energy-dependent step or steps in receptor-operated coupling mechanisms upstream to myosin light chain (MLC) kinase, or (b) by energy limitation of MLC kinase-mediated phosphorylation of the MLC or actin-activated myosin ATPase. 2. Oxidative energy production was rapidly inhibited by decreasing organ bath PO2 to less than 30 mmHg. There was no difference, comparing KCl- or NOR-induced force, in the rates of decrease of [PCr] (phosphocreatine) or [ATP] following inhibition of oxidative energy production. (In this report we use the term [PCr] and [ATP] to indicate mean tissue values). Initial rates of decrease in [PCr] and [ATP] following inhibition of oxidative energy production were 0.05 mM/min and 0.06 mM/min, respectively. 3. Despite similar decreases in mean tissue [PCr] and [ATP], relaxations of KCl-induced contractions following inhibition of oxidative energy production were markedly delayed and were blunted compared to relaxations seen during NOR-induced contractions. The threshold mean tissue [PCr] and [ATP] for relaxation during KCl stimulation were 0.25 and 0.60 to 0.80 mM, respectively. During NOR stimulation, threshold values of [PCr] and [ATP] were 0.50 mM and 0.80 mM, respectively. Mean tissue [PCr] and [ATP] levels at 50% relaxation of KCl-induced force were less than 0.1 mM and 0.1 mM, respectively. Fifty per cent relaxation of NOR-induced force occurred at [PCr] and [ATP] values of 0.35 mM and 0.65 mM, respectively. 4. MLC phosphorylation levels decreased during relaxation of NOR force evoked by inhibition of oxidative energy production. There was no change in the level of MLC phosphorylation following inhibition of oxidative energy production in KCl-contracted muscle even at mean tissue [PCr] and [ATP] lower than values associated with decreases in MLC phosphorylation during relaxations of NOR-induced force. 5. Oxygen-induced redevelopment of force during NOR exposure was not dependent on extracellular Ca2+. Mean tissue [PCr] increased prior to onset of O2-evoked force redevelopment. Increases in MLC phosphorylation were seen at the time of onset of force redevelopment. 6. Oxidative metabolism-contraction coupling during NOR-stimulation seems not to be due to energy limitation of the MLC kinase reaction or actin-activated myosin ATPase. Data suggest the rate-limiting step is an energy-dependent reaction in receptor-operated coupling mechanisms upstream to MLC kinase.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Rate-limiting energy-dependent steps controlling oxidative metabolism-contraction coupling in rabbit aorta. 153 69

The localization of creatine kinase (CK) M in canine myocardium was immunocytochemically studied by a direct immunoperoxidase method. Specific antiserum against CK-M was produced in rabbits immunized with canine CK-MM. An anti-CK-M Fab'-horseradish peroxidase conjugate was prepared by the maleimide method. Frozen sections prepared from fixed canine myocardium were stained with the conjugate and observed by light and electron microscopy. In light microscopy of longitudinal sections, CK-M showed a cross-striated pattern consisting of distinct broad and narrow brown bands. Immunoelectron microscopy revealed that the regions of the broad and narrow brown bands corresponded to the A-band and the Z-line, respectively. Most CK-M in the A-band was associated with the thick fibers, and a small amount of CK-M was found in the M-line. These findings suggest that ATP regeneration from the ADP produced by myosin ATPase is related to the participation of this CK associated with the thick fibers rather than that of the M-line-bound CK. Creatine kinase M was also found in the sarcolemmal membrane, the membranes of the sarcoplasmic reticulum, and the mitochondrial outer and inner membranes. This report provides new information for understanding the physiological role of the phosphorylcreatine shuttle in the myocardial energy transport system.
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PMID:Immunocytochemical localization of creatine kinase M in canine myocardial cells: most creatine kinase M is distributed in the A-band. 277 5

Control of mitochondrial respiration depends on ADP availability to the F1-ATPase. An electrochemical gradient of ADP and ATP across the mitochondrial inner membrane is maintained by the adenine nucleotide translocase which provides ADP to the matrix for ATP synthesis and ATP for energy-dependent processes in the cytosol. Mitochondrial respiration is responsive to the cytosolic phosphorylation potential, ATP/ADP.Pi which is in apparent equilibrium with the first two sites in the electron transport chain. Conventional measures of free adenine nucleotides is a confounding issue in determining cytosolic and mitochondrial phosphorylation potentials. The advent of phosphorus-31 nuclear magnetic resonance (P-31 NMR) allows the determination of intracellular free concentrations of ATP, creatine-P and Pi in perfused muscle in situ. In the glucose-perfused heart, there is an absence of correlation between the cytosolic phosphorylation potential as determined by P-31 NMR and cardiac oxygen consumption over a range of work loads. These data suggest that contractile work leads to increased generation of mitochondrial NADH so that ATP production keeps pace with myosin ATPase activity. The mechanism of increased ATP synthesis is referred to as 'stimulus-response-metabolism' coupling. In muscle, increased contractility is a result of interventions which increase cytosolic free Ca2+ concentrations. The Ca2+ signal thus generated increases glycogen breakdown and myosin ATPase in the cytosol. This signal is concomitantly transmitted to the mitochondria which respond to small increases in matrix Ca2+ by activation of Ca2+-sensitive dehydrogenases. The Ca2+-activated dehydrogenase activities are key rate-controlling enzymes in tricarboxylic acid cycle flux, and their activation by Ca2+ leads to increased pyridine nucleotide reduction and oxidative phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Control of mitochondrial respiration in muscle. 305 Apr 50

The time course of changes of inorganic phosphate (Pi) and phosphocreatine (PCr) was studied during and after brief isometric tetanic contractions using phosphorus nuclear magnetic resonance on isolated semitendinosus muscles of the bullfrog at 4 degrees C. We followed essentially the method of Dawson, Gadian and Wilkie and the signal-to-noise ratio was improved by using many muscles. Immediately following the relaxation of contraction, the fall of PCr was not sufficient to account for the Pi released. The level of PCr remained unaltered, or decreased further, in the early post-contractile period. The amount of Pi that appeared without PCr splitting was similar to the amount of myosin sites (0.3 mmol kg-1 muscle) irrespective of the duration of contraction. The post-contractile utilization of PCr was strongly temperature dependent. It was prolonged at 1 degree C, whereas it almost disappeared at 10 degrees C. When the filament overlap was much reduced by stretching the muscles the phenomenon became undetectable. All these results have indicated that the post-contractile utilization of PCr is closely associated with the actin-myosin ATPase cycle.
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PMID:Time-resolved 31P nuclear magnetic resonance studies on isometric contraction of frog skeletal muscle. 326 89

After prolonged ischemia followed by reperfusion of the isolated rat heart, irreversible heart failure is associated with creatine kinase leakage from the cells. The possible implications of MM creatine kinase leakage from myofibrillar compartments on the contractile properties of ventricular muscle have been studied in control versus ischemic hearts. Total creatine kinase activity decreased in ischemic cells while creatine kinase and ATPase activities were not modified in isolated myofibrils. The efficiency of creatine kinase and phosphocreatine in the relaxation of rigor tension in skinned ventricular preparations was not changed after ischemia. Furthermore, neither the pCa/tension relationship nor the rate of tension development following length changes were modified by ischemia. These results show that the contractile properties of myofilaments as well as the functional coupling between myosin ATPase and creatine kinase are preserved in ischemic hearts suffering irreversible contractile failure.
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PMID:Contractile properties and creatine kinase activity of myofilaments following ischemia and reperfusion of the rat heart. 343 83

The influence of phosphocreatine in the presence or absence of MgATP and MgADP was studied in Triton X-100-treated thin papillary muscles and ventricular strips of the rat heart. The pCa/tension relationships, the pMgATP/tension relationships, and the tension responses to quick length changes were analyzed. The results show three major consequences of the reduction of the phosphocreatine concentration in the presence of millimolar concentrations of the MgATP. (a) The resting tension and the maximal Ca2+-activated tension were increased, and the pCa/tension relationship was shifted toward higher pCa values and its steepness was decreased; these effects were enhanced by the inclusion of MgADP. (b) The time constant of tension recoveries after quick stretches applied during maximal activation was increased, while the extent of these recoveries was decreased. (c) The study of pMgATP/tension relationships in low Ca concentrations showed that the decrease in phosphocreatine induced a shift toward higher MgATP values with no changes in maximal rigor tension or the slope coefficient; these effects were increased by the increase in MgADP and were independent of the preparation diameter. Thus, modifications of the apparent Ca sensitivity and resting and maximal tension when phosphocreatine is decreased seem to be due to an increasing participation of rigor-like or slowly cycling cross-bridges spending more time in the attached state. These results suggest that endogenous creatine kinase is able to ensure maximal efficiency of myosin ATPase by producing a local high MgATP/MgADP ratio.
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PMID:Role of creatine kinase in force development in chemically skinned rat cardiac muscle. 349 24

A modified isolated canine gracilis model of acute complete muscle ischemia was developed and then tested metabolically and histologically in 25 animals to assess its validity. In each dog, both gracili were isolated on their major vascular pedicles. One muscle underwent ischemia and reperfusion by placing and removing microvascular clips on the artery and vein. The other gracilis muscle was used as a control. Total muscle blood flow measurements, blood samples, and muscle biopsies were taken every other hour for up to 11 hr after preparation. The fiber-type profile of the gracilis was determined bilaterally using a myosin ATPase stain (n = 10). The results verified these hypotheses: after surgical preparation, the right and left muscles in the same dog are equivalent metabolically, after a 2-hr stabilization period, gracilis blood flow, oxygen and glucose uptake, lactate release, and tissue glycogen, lactate, phosphocreatine, and ATP levels remain within normal limits and unchanged for the next 9 hr, the surgical isolation of the gracilis muscle on a single vascular pedicle does not result in significant metabolic changes, in this model, a 2-hr ischemia is reversible, but a 7-hr ischemia results in irreversible ischemic injury. As well, fiber-type profile, muscle blood flow, and metabolic parameters can very significantly among animals supporting the necessity of a contralateral control. Therefore, this modified gracilis muscle model with its contralateral muscle as a control is suitable for acute skeletal muscle ischemia experiments of at least 9-hr duration.
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PMID:An isolated skeletal muscle model suitable for acute ischemia studies. 374 95

31P-NMR was used to characterise intracellular phosphate pools and their post mortem changes at 7 degrees C in intact red and white cod muscles under anaerobic conditions. A total phosphate content of 55 and 60 mM was observed in red and white muscle, respectively. The concentration of P-creatine was 14 mM in the white and 9 mM in the red muscle, while that of inorganic phosphate, Pi (30 mM), ATP (9 mM), and sugar phosphate (5 mM) were similar in both muscles. During the first 90 min after death, the decrease in P-creatine showed a first order breakdown with a concomitant stoichiometric increase in Pi content, whereas the ATP and sugar phosphate remained the same. The intracellular pH decreased from 7.4 to 7.3 in this period. The steady-state rate constant of myosin ATPase was 0.0054 and 0.0022/min for red and white muscles, respectively. Individuals kept under diminished oxygen tension prior to being killed, showed a reduced P-creatine level in both muscles.
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PMID:31P-NMR studies of phosphate metabolites in intact red and white swimming muscles of cod (Gadus morhua L.). 375 79

MgADP has a more pronounced effect on the relaxation behaviour in tonic vascular smooth muscle compared to phasic smooth muscle. An apparent dissociation constant of 1.3 microM has been reported for a high affinity binding site of vascular smooth muscle cross-bridges. For this high affinity to have an effect on the low energy costs of tension maintenance (latch) it would require that free [ADP] in the region of the contractile proteins (at least sometimes) be as low as 1.3 microM. We ask, in this report, whether [ADP] could be as low as 1.3 microM in vascular smooth muscle. If creatine kinase (CK) is at equilibrium, then micromolar [ADP] is incompatible with measured concentrations of phosphocreatine (PCr), free creatine (Cr) and ATP, which entail a mean equilibrium [ADP] of around 18 microM. But CK may not be quite at equilibrium: if there is net PCr synthesis at the mitochondrion, then maintenance of the steady-state requires that there be net PCr hydrolysis in the region of the contractile proteins up to or equal to the rate of myosin ATPase. We derive a simple relationship between net flux and displacement from equilibrium which we use to argue that an [ADP] of 1.3 microM at the contractile proteins would drive significant net PCr synthesis, incompatible with normal contractile function. Thus the CK system holds [ADP] at about 18 microM near the contractile proteins in vascular smooth muscle. We conclude that smooth muscle [ADP] cannot be far from equilibrium and that a role for ADP (at the low micromolar level) in controlling smooth muscle relaxation is unlikely.
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PMID:The creatine kinase equilibrium, free [ADP] and myosin ATPase in vascular smooth muscle cross-bridges. 773 20


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