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:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A Dictyostelium mutant (7-11) that expresses less than 0.5% of wild-type levels of the myosin essential light chain (EMLC) has been created by overexpression of antisense RNA. Cells from 7-11 contain wild-type levels of the myosin heavy chain (MHC) and regulatory light chain (RMLC). Myosin isolated from 7-11 cells consists of the MHC with the RMLC associated in reduced stoichiometry, and binds to purified actin in an ATP-sensitive fashion. Purified 7-11 myosin displays calcium-activated ATPase activity with a Vmax about 15%-25% of that of wild type, and a Km for ATP of 27 +/- 5 microM versus 83 +/- 30 microM for wild type. At actin concentrations as high as 17 microM, 7-11 myosin displays greatly reduced actin-activated ATPase activity. Phenotypically, 7-11 cells resemble MHC mutants, growing poorly in suspension and becoming large and multinucleate. When starved for multicellular development, 7-11 cells take several hours longer than wild-type cells to aggregate. Although multicellular aggregates eventually form, they fail to develop further. The cells are also unable to cap receptors in response to Con A treatment. Since cells expressing the EMLC are phenotypically similar to MHC null mutants, the EMLC appears necessary for myosin function, at least in part because it is required for normal actin-activated ATPase activity.
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PMID:The Dictyostelium essential light chain is required for myosin function. 153 25

The purpose of this study was to determine if selected biochemical parameters representing the contractile and calcium regulating systems of cardiac muscle scaled among mammals having inherently different resting heart rates (RHR). Eight mammalian species with RHR ranging from 51 to 475 beats per minute (bpm) were studied. The oxidative capacity of the myocardium is highly correlated with the RHR. The hypothesis of the present study was that the capacities of the energy utilizing processes of contraction and calcium regulation would also be correlated to the functional demand imposed on the muscle as represented by the RHR. Myosin (M) and myofibrillar (MF) ATPase activities, myosin isoenzyme distribution and sarcoplasmic reticulum (SR) ATPase activity were determined. Animals with RHR above 300 bpm express V1 myosin while animals with lower RHR express primarily V3. M and MF ATPase activities correlated with RHR, but the major difference in activities occurred at the 'threshold' RHR of about 300 bpm at which the switch from V3 to V1 appears to occur. SR ATPase activity per mg of microsomal protein was for the most part constant among different mammals, but the SR ATPase activity per g of heart tissue was significantly correlated with RHR as slower beating hearts tended to yield less SR protein per unit mass. We conclude that both the contractile and calcium regulating systems are scaled to the functional parameter of RHR among different mammals. The contractile system uses a slow myosin ATPase isoform at low resting heart rates whereas above the postulated threshold RHR of about 300 bpm a switch in gene expression to a fast myosin ATPase isoform occurs.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Contractile and calcium regulating capacities of myocardia of different sized mammals scale with resting heart rate. 165 10

Myosin ATPase activity was measured, by continuous luminometric method, in presence of different molecular weight heparins. ATPase activity decreases in the presence of heparin, when simultaneous incubation with ATP is carried out; the percentage of inhibition is proportional to polysaccharide concentration. Heparins of different molecular weights (1.75 KD to 11.6 KD) are competitive inhibitors of enzymatic activity; the inhibitory effects is also appreciable with trisulphated disaccharide. The possible mechanisms of interaction between heparin and myosin ATPase are discussed.
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PMID:Competitive inhibition of myosin ATPase activity by different molecular weight heparins. 165 81

1. Isometric twitch and tetanic tensions were recorded from whole muscles and single motor units in fourth deep lumbrical muscles isolated from young adult (60 days) rats. Muscles were superfused with oxygenated Ringer solution at 25 degrees C except where stated otherwise. 2. It was confirmed that the muscle is supplied most commonly by eleven motor axons, nine via the lateral plantar nerve (LPN), and two via the sural nerve (SN). Motor units whose axons were isolated from either LPN or SN were studied. There was no difference in mean motor unit size. 3. In their unfused tetani most units showed 'sag' and some 'no sag', with no segregation between LPN and SN. 'No sag' units were always small (unit tetanic tension less than 8% whole-muscle tetanic tension), tended to be relatively slowly contracting and relaxing during an isometric twitch, and tended to have relatively low twitch:tetanus ratios. Units showing sag ranged from large to small. 4. In some motor units muscle fibres were depleted of their glycogen by repetitive stimulation at 30 degrees C in glucose-free Ringer solution, and the muscle and its unstimulated control frozen and sectioned. Neighbouring sections were stained for glycogen and for binding of two myosin-specific antibodies, one specific for slow myosin and the other for type IIA myosin. Myosin ATPase and succinic dehydrogenase histochemistry were also carried out in some muscles. 5. Serial reconstructions showed that all or virtually all extrafusal fibres in the muscle were present in a midbelly section, and that the myosin type of individual fibres did not change significantly along their length. Spindle profiles were seen frequently and in two muscles eight and twelve spindles were identified. 6. Of twenty-six motor units examined twenty contained almost exclusively muscle fibres of the recently described type IIX. All these units showed sag in their isometric tetani. 7. Six units each contained 50% or more of slow myosin-containing fibres (IIC and a few type I). The remaining fibres in these units were IIA. All these units were therefore of mixed fibre composition, and are discussed as IIC/IIA units. In whole muscles slow-myosin-containing fibres were generally distributed evenly (non-randomly) throughout the muscle cross-section. 8. Whole muscles contained on average 970 fibres (S.D. +/- 70) of which 82 (+/- 9) were slow-myosin-containing. A few muscles from older rats (3-24 months) contained very few such fibres.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Motor units of the fourth deep lumbrical muscle of the adult rat: isometric contractions and fibre type compositions. 182 26

Brush border myosin I from chicken intestinal microvilli is a membrane-associated, single-headed myosin composed of a 119-kDa heavy chain and several calmodulin light chains. We first describe in detail a new procedure for the rapid purification of brush border myosin I in greater than 99% purity with a yield of 40%, significantly higher than for previous methods. The subunit stoichiometry was determined to be 4 calmodulin light chains/myosin I heavy chain by amino acid compositional analysis of the separated subunits. We have studied the effects of Ca2+ and temperature on dissociation of calmodulin from myosin I and on myosin I Mg2(+)-ATPase and contractile activities. At 30 degrees C the actin-activable ATPase activity is stimulated 2-fold at 10-700 microM Ca2+. Dissociation of 1 calmodulin occurs at 25-50 microM Ca2+, but this has no effect on actin activation. The contractile activity of myosin I, expressed as superprecipitation, is greatly enhanced by Ca2+ under conditions in which 1 calmodulin is dissociated. This calmodulin is thus not essential for actin activation or superprecipitation. Myosin I was found to be highly temperature-sensitive, with an increase to 37 degrees C resulting in dissociation of 1 calmodulin at below 10(-7) M Ca2+ and an additional 1.5 calmodulins at 1-10 microM Ca2+. A complete loss of actin activation accompanies the Ca2(+)-induced calmodulin dissociation at 37 degrees C. Our conclusion is that physiological levels of Ca2+ can either stimulate or inhibit the mechanoenzyme activities of brush border myosin I in vitro, with the mode of regulation determined by the number of associated calmodulin light chains.
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PMID:Ca2+ stimulates the Mg2(+)-ATPase activity of brush border myosin I with three or four calmodulin light chains but inhibits with less than two bound. 182

Cardiological findings in athletes are often similar to those observed in clinical cases. Electrocardiographic and cardiac imaging abnormalities as well as physical findings may be the same in both of these groups. Bradycardia and rhythm disturbances are the most common abnormalities in athletes. Most athletes with abnormal electrocardiograms are asymptomatic and numerous investigators have failed to detect heart disease in association with such electrocardiograms. In contrast to cardiac dysfunction observed in clinical cases, enhanced or normal ventricular systolic and diastolic function have been reported in athletes. In endurance athletes, this is associated with very high values for maximal aerobic power (VO2max). Absolute and body size-normalised cardiac dimensions in most athletes do not approach values from chronic disease states, and may not exceed echocardiographic normal limits. In addition, pathological and physiological enlargement appear to be biochemically and functionally different. Myosin ATPase enzyme expression and calcium metabolism are different in rats with pathologically or physiologically induced enlargement. The reported biochemical differences underlie systolic and diastolic dysfunction in pathological enlargement. Conversely, trained rodents and humans have demonstrated enhanced systolic and diastolic function. It is important to note that cardiac enlargement observed in athletes is the result of normal adaptation to physical conditioning and/or hereditary influences. Conversely, pathological changes result from disease processes which can lead in turn to reduced function, morbidity and mortality. Since the mid 1970s echocardiography has been used to compare cardiac dimensions in male endurance- and resistance-trained athletes. A sport-specific profile of eccentric and concentric enlargement has been documented in endurance and resistance athletes, respectively. Subsequent studies of athletes have examined factors such as age, sex and degree of competitive success to determine their contribution to these sport-specific cardiac profiles. Unique athletic subgroups have also been analysed and have included ballet dancers, rowers, basketball players and triathletes. However, there is a paucity of data on cardiac dimensions in female athletes. Finally, physical conditioning studies have also examined echocardiographic dimensions before and after endurance and resistance training. Significant enlargement of internal dimensions, wall thickness or left ventricular mass have been reported but such increases are relatively small and by no means universal. Several conflicting explanations for enlarged cardiac dimensions appear in the literature. Chronic volume and pressure haemodynamic overloading during physical conditioning has been proposed to explain eccentric and concentric cardiac enlargement in endurance- and resistance-trained athletes respectively. However, twin studies suggest that hereditary factors may be important determinants of cardiac dimensions and/or the degree of cardiac adaptability to physical conditioning.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The 'athletic heart syndrome'. A critical review. 182 49

Myosin from molluscan adductor muscle is regulated directly by Ca2+ binding. In the absence of Ca2+ the ATPase activity is greatly inhibited. We review the application of transient kinetic methods to this system and show how they can be simple to perform and less ambiguous than steady-state methods.
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PMID:Kinetic analysis of regulated myosin ATPase activity using single and limited turnover assays. 183 60

The purpose of this study was to determine whether cardiac biochemical adaptations are induced by chronic exercise training (ET) of miniature swine. Female Yucatan miniature swine were trained on a treadmill or were cage confined (C) for 16-22 wk. After training, the ET pigs had increased exercise tolerance, lower heart rates during exercise at submaximal intensities, moderate cardiac hypertrophy, increased coronary blood flow capacity, and increased oxidative capacity of skeletal muscle. Myosin from both the C and ET hearts was 100% of the V3 isozyme, and there were no differences between the myosin adenosine triphosphatase (ATPase) or myofibrillar ATPase activities of C and ET hearts. Also, the sarcoplasmic reticulum Ca(2+)-ATPase activity and Na(+)-Ca2+ exchange activity of sarcolemmal vesicles were the same in cardiac muscle of C and ET hearts. Finally, the glycolytic and oxidative capacity of ET cardiac muscle was not different from control, since phosphofructokinase, citrate synthase, and 3-hydroxyacyl-CoA dehydrogenase activities were the same in cardiac tissue from ET and C pigs. We conclude that endurance exercise training does not provide sufficient stress on the heart of a large mammal to induce changes in any of the three major cardiac biochemical systems of the porcine myocardium: the contractile system, the Ca2+ regulatory systems, or the metabolic system.
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PMID:Biochemical characterization of exercise-trained porcine myocardium. 183 67

The mechanisms by which the aged heart adapts to a superimposed pressure load such as hypertension have not been described. We therefore investigated biochemical and molecular genetic adaptations in the 24-month-old rat heart subjected to renovascular hypertension. Compared with 4-month-old rats, aging was associated with a 68% increase in left ventricular mass without any change in heart weight-to-body weight ratio, a 33% reduction in calcium-activated myosin ATPase activity, and a shift from a V1 to a V3 predominant myosin heavy chain (MHC) isoform distribution. A 46% reduction in alpha-MHC mRNA and a reciprocal increase in beta-MHC mRNA was seen. When hypertension was superimposed, there was a further 75% increase in ventricular mass, a 63% increase in heart weight-to-body weight ratio, and a 19% reduction in myosin ATPase. Myosin isozyme distribution was further shifted to V3, and the ratio of alpha-MHC to beta-MHC mRNA was reduced. In addition, with hypertension a significant (greater than 50%) reduction in the mRNA level of the cardiac sarcoplasmic reticular calcium-activated ATPase was seen. These data demonstrate that the aged myocardium is able to respond to a superimposed pressure load with a molecular genetic and protein synthetic pattern of hypertrophy analogous to that seen in younger animals.
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PMID:Effect of aging and hypertension on myosin biochemistry and gene expression in the rat heart. 183 8

After myocardial infarction in rats, muscle performance in the remaining hypertrophied myocardium deteriorates and is associated with a decrease in myosin adenosinetriphosphatase (ATPase) activity and a shift to the V3 myosin heavy-chain isoform. We have previously shown in another model of hypertrophy, secondary to renovascular hypertension, that chronic intermittent adrenergic stimulation with dobutamine (Db) can prevent this biochemical adaptation. The present study was undertaken to assess the effects of chronic Db treatment on cardiac mass, function, metabolism, and myosin biochemistry in animals subjected to chronic myocardial infarction. Four groups of rats were studied: controls, animals treated with Db (2 mg/kg 2X daily for 4 wk), animals subjected to myocardial infarction and killed after 4 wk (MI), and MI animals concurrently treated with Db for 4 wk (MI-Db). The two MI groups were subdivided into those with and without congestive heart failure (CHF). Heart weight was increased by 13% with Db, unchanged in the infarct groups without CHF, and increased by 9 and 22% in the infarct groups with CHF. Db did not have any additional effect on heart weight in these later groups. Infarct weight was greatest in the animals with CHF, and viable myocardium was equivalent in all infarct groups suggesting that CHF was associated with a greater degree of hypertrophy. Ventricular performance, as assessed in an isovolumic heart apparatus, was markedly depressed in both infarct groups with CHF and was not affected by Db. Db increased myosin ATPase activity in control and infarcted animals both with and without congestive heart failure. Myosin oxygen consumption and lactate production were not adversely affected by Db.
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PMID:Effects of chronic dobutamine on cardiac mechanics and biochemistry after myocardial infarction in rats. 199 90


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