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)

Studies were made on the effect of thyroid hormones on the level of acetylcholine receptors (AChR) in cultured rat skeletal muscle. Treatment of differentiated myotubes in vitro with thyroxine (T4; 2 X 10(-7) mol/l) for 2-3 days caused a marked decrease in the amount of AChR (P less than 0.05) and an increase in activity of Na+-K+-ATPase (P less than 0.05). There was no significant effect of hormone treatment on other muscle proteins, such as creatine kinase and acetylcholinesterase. Measurements of the turnover rate of AChR in T4-treated myotubes showed only a very slight effect of T4 on the rate of AChR degradation. To study the mechanism by which the hormone exerts its effect, muscle cells were labelled with radioactive amino acid and the rate of its incorporation into AChR protein was measured. The AChR was then isolated using anti-AChR antibodies. The specific activity of labelled AChR was lower in hormone-treated cells. These experiments suggest that the decreased level of AChR in response to thyroid hormone treatment is due to a partial suppression of receptor synthesis.
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PMID:Inhibition of acetylcholine receptor synthesis by thyroid hormones. 620 79

The spontaneous contractions of cultured chick skeletal muscle fibers were abolished by growth of cultures in the presence of tetrodotoxin (TTX). Inhibition of the contractile activity of cultured myofibers was associated with a marked reduction in the rate of azide-insensitive, ATP-dependent Ca2+ uptake by the total particulate fraction of cell homogenates and by purified sarcoplasmic reticulum. Myosin heavy chain (MHC) accumulation and azide-insensitive, ATP-dependent Ca2+ uptake into a total cell membrane fraction were measured simultaneously in the same culture dish. A decrease in the activity of the ATP-dependent Ca2+ uptake system preceded a significant reduction in MHC content of contraction-inhibited cultures. The reduced rate of Ca2+ uptake observed in the sarcoplasmic reticulum from TTX-treated cultures paralleled a decrease in the amount of enzymatically active Ca2+-transport ATPase. The cellular concentration of the ATPase was estimated from a measurement of the concentration of the Ca2+-dependent, hydroxylamine-sensitive, steady state level of phosphorylated intermediate formed in culture microsomes. In contrast to the changes observed in activity of the sarcoplasmic reticulum ATPase and MHC content of TTX-treated cultures, neither the specific activity of creatine kinase nor the accumulation of the MM isoenzyme were affected. It is therefore concluded that the contractile activity of muscle has a selective effect on the maintenance of the adult skeletal muscle phenotype.
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PMID:Effect of tetrodotoxin relaxation of cultured skeletal muscle on the sarcoplasmic reticulum Ca2+-transport ATPase. 622 Sep 16

A creatine kinase assay based on estimation of creatine liberated from creatine phosphate was accurate and reproducible for use with seminal or prostatic fluid, after allowance was made for acid phosphatase interference. Comparison of this method with one which relies on enzymic coupling of ATP formation to NADP+ oxidation shows that the latter under-estimates creatine kinase activity by a factor of about 3. This discrepancy could be due to the high ATPase activity found in prostatic and seminal fluid. Uncritical use of the NADP+ assay might account for different seminal creatine kinase values reported in the literature. Interrelationships between ATPase, creatine kinase and zinc suggest that seminal ATPase is a prostatic secretory product while creatine kinase may be multiglandular in origin.
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PMID:Creatine kinase and ATPase in human seminal fluid and prostatic fluid. 622 Oct 96

The participation of the intracellular creatine kinase system in energy transport in cardiac cells was studied further. The functional behavior of different but kinetically indistinguishable isoenzymes of creatine kinase (CK) in muscle cells is determined by their intracellular localization as is shown in this report for mitochondrial and sarcolemmal creatine kinases. The kinetics of the forward mitochondrial creatine kinase reaction is influenced by oxidative phosphorylation which increases the apparent affinity for ATP but does not change the kinetics of the reverse creatine kinase reaction. The molar content of creatine kinase in heart mitochondria was determined and found to be close to the content of adenine nucleotide translocase, thus supporting the concept of the tight functional relationship between those two mitochondrial proteins as a basis for effective phosphocreatine (PCr) production in mitochondria. In the sarcolemmal preparation, the antiport of Na+ and K+ is much more effectively supported by the sarcolemmal creatine kinase reaction than by an externally added ATP-regenerating system consisting of phosphoenolpyruvate and pyruvate kinase. The results of these experiments are taken to show the ability of sarcolemmal creatine kinase to maintain a very high phosphorylation potential in the vicinity of the active centers of the Na+ -K+ ATPase necessary to support the active transport of Na+ and K+ across the plasma membrane and to avoid a reversal of the ion gradient. Finally, it is concluded in this chapter that a rapid decrease in PCr content in the cells under anoxic or ischemic conditions may be one of the important factors in the impairment of cardiac contractile function under those conditions.
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PMID:Intracellular energy transport and control of cardiac contraction. 622 78

Male Fischer rats of four age groups were subjected to a 3-mo exercise training program that consisted of a gradual increase to 1 h/day of forced swimming. Exercise was initiated at 1, 6, 12, or 17-22 mo of age. After the training period there was an increase in the heart weight relative to body weight in all groups, but heart weight was increased only in the two oldest groups. The specific activities of both actomyosin ATPase and creatine kinase isolated from cardiac muscle decreased with age. In animals that started exercise training at 6 mo of age the activities of both enzymes were higher than that of the age-matched sedentary controls, but the oldest animals (17-22 mo) responded negatively (i.e., a decreased enzymatic activity compared with sedentary individuals of the same age). These results suggest that, after a certain age, the initiation of endurance exercise may not result in the same adaptive response as occurs in younger animals. In the case of actomyosin ATPase this may be a consequence of a different distribution of myosin isozymes.
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PMID:Effect of physical training on myocardial enzyme activities in aging rats. 622 30

The behavior of several enzymes was studied during rat heart development (4 days before birth to adult stage). Hexokinase has its highest activity during the fetal period; it decreases at birth and remains with low activity in the adult. The alpha-glycerophosphate dehydrogenase and alpha-glycerophosphate oxidase profiles are similar up to the 15th day of development. From there onwards, both profiles diverge, the cytoplasmic activity increasing 3-fold, while the mitochondrial activity remains unchanged. The developmental profiles of the malate dehydrogenases are almost parallel. The development of citrate synthase and succinate dehydrogenase results in a 2- to 4-fold increase in their activities. However, ATPase increases dramatically (20-fold) over the same period. With respect to the enzymes of the adenine nucleotide metabolism, adenylate kinase is fully expressed throughout all ages examined, showing no variation during development. AMP deaminase and creatine kinase increase during development, the cytoplasmic creatine kinase reaching a high level at birth whereas the increases of the mitochondrial enzymes take place gradually during development.
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PMID:Development of enzymes of energy metabolism in rat heart. 623 Jan 12

In isolated and purified cardiac myofibrillar and sarcolemmal preparations, the route of movement of ADP produced in the Mg2+-ATPase reactions was studied by investigating the efficiency of competition between the endogenous creatine kinase and exogenous pyruvate kinase reactions. In the homogeneous control system composed of hexokinase and glucose as ATPase, soluble creatine kinase rapidly rephosphorylated ADP produced in the presence of 1 mM ATP, but the addition of pyruvate kinase in an increasing amount inhibited the reaction of creatine release from phosphocreatine and symmetrically increased the rate of pyruvate production from phosphoenol pyruvate. At a pyruvate-kinase/creatine-kinase activity ratio (PK/CK) of 50, all ADP was used by the pyruvate kinase. In myofibrillar and sarcolemmal preparations containing particulate creatine kinase, the creatine kinase reaction was much less efficiently suppressed by pyruvate kinase, and at PK/CK = 50 half-maximal release of creatine was still observed. The rate of immediate myofibrillar MgADP rephosphorylation in the endogenous creatine-kinase reaction was observed to be governed by the concentration of phosphocreatine in accordance with the kinetics of this enzyme. The physiological significance of these findings is discussed.
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PMID:Creatine kinase in regulation of heart function and metabolism. I. Further evidence for compartmentation of adenine nucleotides in cardiac myofibrillar and sarcolemmal coupled ATPase-creatine kinase systems. 623 Oct 56

Isometric contraction and relaxation of glycerinated rabbit psoas muscle fibers containing native creatine kinase (CK) and ATPase activities were studied. Energy for contraction and relaxation was provided either by ADP + creatine phosphate (CP) or ATP alone, and the effectiveness of these additions on rate and maximum force of contraction and relaxation were compared. In the presence of 250 microM ADP, physiological concentration of CP (10 mM) produced faster and stronger contraction and faster and more complete relaxation than equimolar or even higher concentrations of ATP. When contraction was initiated by addition of ADP to fibers preincubated with 10 mM CP, the apparent Km for ADP was 1.18 +/- 0.24 mM. If the fibers were preincubated with ADP and contraction initiated by addition of 10 mM CP, the apparent Km for ADP was more than an order of magnitude smaller (76.0 +/- 4 microM). The observed Km for ADP for contraction was about half the Km for CP in solution (151.5 microM). The apparent Km for CP for rate of contraction was 2.67 +/- .046 mM independent of sequence of addition of ADP. Since these experiments were done in the presence of P1,P5-diadenosine 5'-pentaphosphate, a powerful inhibitor of adenylate kinase, the role of this enzyme in the process was not significant. These observations support the idea of compartmentation of myofibrillar CK in close function with myosin ATPase as part of the phosphoryl creatine energy shuttle.
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PMID:Myofibrillar end of the creatine phosphate energy shuttle. 623 38

The possible role of the intracellular creatine kinase system in energy transport and in the metabolic control of ion fluxes across the cardiac cell membranes has been studied. The experimental data reported indicate that creatine kinases bound to the sarcolemmal membrane and to the membrane of sarcoplasmic reticulum are coupled to Na+, K+-ATPase and Ca2+-ATPase, respectively, and ensure rapid rephosphorylation of ADP produced in the ATPase reactions, maintaining a high and constant ATP:ADP ratio near the active centers of ATPases. The ability of creatine phosphate to increase the rate of activator calcium entry across the surface membrane into cardiac cells has been experimentally demonstrated. It is concluded that the intracellular creatine kinase system can exert metabolic control of heart muscle contraction.
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PMID:Energy metabolism and ion fluxes across cardiac membranes. 624 31

A highly purified sarcolemmal fraction from rat heart consisted of closed inside-out oriented vesicles and possessed high activities of Na+, K+-ATPase, adenylate cyclase and creatine kinase. Contaminations of sarcolemmal preparation by other membranous fractions were practically absent. This sarcolemmal fraction contained protein kinase tightly bound to the membrane. Substrates of the phosphorylation reaction catalyzed by this protein kinase were either endogenous sarcolemmal protein (proteins) with molecular weight of 11500 or exogenous protein--histone, type II. Phosphorylation of the endogenous but not of the exogenous substrate was completely independent of cyclic AMP. A kinetic analysis of the sarcolemmal protein kinase reaction with Mg[gamma-32P]ATP and histone as substrates revealed that the kinetic mechanism of this reaction is characterized by the following kinetic parameters: Km (Mg-ATP) = 12.1 microM; Km (histone) = 0.47 mg/ml; Ki (Mg-ADP) = 15.6 microM. A comparison of experimental results to literary data allows to suggest that the sarcolemmal enzyme is virtually soluble protein kinase tightly bound to the sarcolemma.
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PMID:[Some properties of the reaction catalyzed by protein kinase bound to cardiac sarcolemma]. 627 Dec 67


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