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)

We tested an assay system introduced for plasma glycoside measurements, basing on the displacement of 3-H-ouabain from Na+-K+-ATPase by unlabeled glycoside. ATPase preparations from hog, cat and guinea pig were used. Displacements were performed using 20 cardiac glycosides, genins and derivatives with different cardiac activity. Most of the glycosides and derivatives do not induce a continuous 3-H-ouabain displacement from the ATPase, but a very steep increase of unbound 3-H-ouabain between 10-minus 7 and 2 times 10-minus 7 M. Therefore this assay system shows a satisfactory discrimination only in a short concentration range. This behavior and a relatively low sensitivity make the ATPase displacement assay problematic for clinical and pharmacokinetical plasma glycoside measurements.
Basic Res Cardiol
PMID:Studies on a plasma cardiac glycoside assay based upon displacement of 3-H-ouabain from Na+-K+-ATPase. 12 69

Under certain conditions the specific ATPase activity of myosin of a given muscle can be altered. The cause of this alteration can only lie in the myosin molecule itself. To produce an enzymatic activity of myosin, an interaction between their light and heavy chains is necessary. However, the specific activity appears to be determined mainly by light chains. Hence, one ought also to look for a basis of the changed activity in changes of the subunits of myosin. There are strong indications that the alterations in specific activity are accompanied by changes in the relative stoichiometry of the essential light chains of the respective myosin preparation. They differ in their pattern of subunits. The specific activity of a given kind of myosin seems to be determined by the combination of their light chains. Thus, a close correlation exists between these two properties of myosin (ATPase activity and structure of its molecule). There are sufficient indications, that these two properties of myosin correlate also with the mechanical capabiltiy of the corresponding muscle. Particularly the results of cross innervation studies demonstrate a close correlation between these three properties in skeletal muscle. The single subunits of myosin are produced and degraded independently and at heterogenous rates. The synthetis of these subunits is significantly accelerated in response to work overload. Thus, it is quite likely that the individual chains are non-coordinately synthesized, giving rise to variations in the relationship of different molecule types of myosin with different specific ATPase activity. Hence, the control mechanism to synthesize the individual subunits could also be the regulative mechanism to produce a myosin of the specific ATPase activity appropriate to the activity pattern of tissue.
Basic Res Cardiol
PMID:Editorial: Subunits of myosin. Relations to ATPase activity and mechanical function of muscle. 12 46

Fatty acids increase the coronary flow rate of rat hearts, perfused according to the Langendorff technique. Long-chain and medium-chain fatty acids are more effective vasodilators than short-chain fatty acids. The vasodilatation by fatty acids does not proceed through the intermediate formation of the vasodilator adenosine, nor by stimulation of adenylcyclase activity. Since at low Ca2+ concentrations fatty acids not only stimulate the coronary flow rate but also cardiac contractility, it is suggested that especially the lipophilic fatty acids have calcium ionophoric properties leading to increased Ca2+ removal from smooth muscle cytosol and hence to vasodilatation. Preliminary experiments, moreover, indicate that both medium- and long-chain fatty acids, like prostaglandin E1 and Ca2+, inhibit membrane ATPase(s) of aorta smooth muscle cells, suggesting increased Ca2+ binding to vascular smooth muscle cell membranes.
Basic Res Cardiol
PMID:Coronary vasodilation by fatty acids. 13 47

The effects of a moderate physical training program on the hearts of rats have been studied. The mechanical responses of these hearts are improved. Possible contributing factors in this improvement are increased coronary reserve and capacity to deliver oxygen to the myocardium, increased myocardial glycogen stores and increased turnover of fatty acids through the endogenous triglyceride pool. Myocardial oxidative compounds and high energy phosphate stores are not altered. Major changes are found in the energy utilization pathways. Actomyosin, myosin, and heavy meromyosin ATPase activity and binding activity of isolated sarcoplasmic reticulum are all enhanced. Sulfhydryl control of the active site of myosin ATPase is altered. The biochemical effects of conditioning are short lived when training is decreased or discontinued.
Adv Cardiol 1976
PMID:Effects of physical training and detraining on intrinsic cardiac control mechanisms. 13 72

In the course of MG-dependent ATP splitting by heart actomyosin, an "energy rich" actomyosin-ADP complex is formed, which promotes the incorporation of phosphate 32P into ATP in myofibrils. The rate of this ATP-phosphate exchange reaction depends on the extent of actin-myosin overlap which can be decreased by stretching glycerinated muscle fibres. In heart muscle, the calcium-ion dependence of this reaction is similar to that of the actomyosin ATPase, the tension, and "immediate fibre stiffness" (which is "hookean" and which is a measure for the number of myosin cross-bridges attached to and interacting with actin). These findings suggest that calcium increases the amount of "contractile" actomyosin-ADP complexes. The proportionality between tension and ATPase activity further suggests that the rate-limiting step of the cross-bridge cycle (which determines the molecular turnover number, the "Wechselzahl" of the ATPase) is only little affected by calcium ions. These ions act by recruiting more bridges rather than by accelerating their reactions. In addition, the depressing effect of inorganic phosphate on the contractile tension and its presumable role in energetic insuffciency will be discussed.
Basic Res Cardiol
PMID:Ca++ activation of ATPase activity, ATP-Pi exchange, and tension in briefly glycerinated heart muscle. 14 Jun 54

In the presence of the regulatory protein complex tropomyosin-troponin ATPase activity of vertebrate skeletal muscle actomyosin is either higher or lower than in the absence of tropomyosin-troponin. The actual behavior depends on ionic strength, Ca2+ concentration, ATP concentration (determining the amount of rigor complexes present), and the ratio between actin and myosin. This effect of the myosin-actin ratio implies that under certain conditions cooperativity in actin-myosin interaction can be seen.
Basic Res Cardiol
PMID:Regulation of actin-myosin interaction. 14 Jun 53

Based on mechanical, biochemical and electron microscopic studies performed in the same stage of experimental cardiac hypertrophy, an attempt is made to define the significance of individual factors responsible for the alterations in myocardial function. Using swimming rats, it is demonstrated that a load-induced increase in cardiac mass is not necessarily connected with an impairment of contractile capability on a cellular level. Yet, also, the reduction of specific ATPase activity and unloaded shortening velocity in pressure-induced hypertrophy (goldblatt rats; aortic stenosis) seems to be the expression of adaptation rather than of cellular damage, at least in the earlier stages. Although there are distinct indications of alterations in Ca-dependent activation and deactivation, in the Goldblatt model electromechanical coupling does not seem to be the main cause of altered contraction parameters. The correlation between specific ATPase activity of actomyosin and unloaded shortening velocity as well as the persistance of decrease in shortening velocity, also under optimal electromechanical coupling conditions, point to an inner relationship between the two values. A discrepancy between unloaded shortening velocity on the one hand and developed tension on the other is mainly due to an increased content of contractile structures. In later stages, an increased connective tissue content influences both isometric and isotonic parameters.
Basic Res Cardiol
PMID:Myocardial function in different models of cardiac hypertrophy. An attempt at correlating mechanical, biochemical, and morphological parameters. 14 Jun 58

The reversal of the calcium pump of cardiac sarcoplasmic reticulum (SR) prepared from dogs was investigated. Phosphorylation of the calcium transport ATPase by orthophosphate and ATP synthesis from ADP and orthophosphate by SR passively preloaded with calcium are demonstrated. The ADP-dependent calcium efflux from SR loaded with calcium in the presence of acetylphosphate is stoichiometrically coupled to ATP synthesis from ADP and orthophosphate.
Basic Res Cardiol
PMID:The reversal of the calcium pump of cardiac sarcoplasmic reticulum. 14 Jun 56

In Goldblatt rats (GV) 4-24 weeks after coarctation of one renal artery the following characteristics were registered as compared to controls (CV) of the same age: Arterial blood pressure increased to 190-200 mmHg in comparison to 105-110 mmHg in controls. This pressure overload induced an increase in ventricular weights (34%-54%). Noteworthy differences in myocardial water, total protein, and nonprotein substance contents were found. Hydroxyproline concentration in GV did not increase significantly until 24 weeks after onset of pressure overload. No significant alterations were detected in the relationship of myocardial, sarcoplasmic, and stromal protein fractions. However, greater changes could be registered in the concentration of the myofibrillar protein fraction and its single components. Furthermore, a correlative depression in specific actomyosin ATPase activity and in maximum shortening velocity of the unloaded cardiac muscle (2,3) was observed.
Basic Res Cardiol
PMID:Characteristics of the hypertrophied left ventricular myocardium in Goldblatt rats. 14 Jun 72

Cell membranes contain special binding proteins for hormones and drugs. These binding sites ("receptors") located on the outside surface are linked to or are part of an enzyme facing the inner side of the membrane and are transducing and probably amplifying the information carried by the pharmacological agent to the cell. As the first step of their action cardiac glycosides reversibly bind with high affinity to specific receptors in cardiac cells and by this inhibit the (Na+ + K+)-ATPase, which is the enzyme system responsible for the active transmembraneous transport of sodium and potassium. It is thought that the inhibition of this active cation transport precedes the positive inotropic effect. Cardio-inactive glycosides have but low affinity to this receptor and thus do inhibit the (Na+ + K+)-activated ATPase only at very high concentrations. The characterization of the cardiac glycoside-receptor interaction in the heart reveals several factors that influence the affinity of the binding sites for the glycosides and thereby determine the sensitivity to this widely used group of potent drugs.
Basic Res Cardiol
PMID:Cell membrane receptors for cardiac glycosides in the heart. 14 74


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