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

---

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

A mixture of purified muscle glycolytic enzymes was reconstituted and the mixture shown to behave in a fashion analogous to that occurring in vivo. Glycolysis leads to ATP production in muscle and results in the phosphorylation of creatine. The extent of this phosphorylation by anaerobic glycolysis was shown to depend to a small extent on the relative proportions of available P(i) and creatine initially, but more importantly on the first step in glycolysis, in this case the enzyme phosphorylase. With less than 0.1% of the phosphorylase in the a form, only about one-third of the creatine was phosphorylated in 30min, whereas with 4% or more of phosphorylase a, 90% of the creatine was phosphorylated within this time. Inclusion of an adenosine triphosphatase decreased the steady-state concentration of phosphocreatine in the system. Calculations of the theoretical concentrations of ADP and AMP showed that phosphorylase b was almost inactive even in the presence of 9mum-AMP, because of ATP inhibition. With phosphorylase a present, glycolysis was able to continue at least until the calculated concentration of MgADP(-) was only 7mum, and AMP in the sub-mumolar range. The relation of these values to measured concentrations of nucleotides and to phosphorylase a percentages in intact muscle is discussed.
...
PMID:Studies with a reconstituted muscle glycolytic system. The rate and extent of creatine phosphorylation by anaerobic glycolysis. 426 7

By using a reconstituted glycolytic system and a highly active adenosine triphosphatase (ATPase), the metabolism during muscular tetanic contraction was simulated and observed. With an ATPase activity somewhat greater than can be maintained in muscle tissue, phosphocreatine was rapidly and completely utilized, lactate production commenced about 5s after the ATPase was added and after 15s adenine nucleotides were lost through deamination to IMP. By 40s, all metabolism ceased because of complete loss of adenine mononucleotides. With a lower ATPase activity, glycolytic regeneration of ATP was capable of maintaining the ATP concentration at its initial value and even by 80s, only one-half of the phosphocreatine had been utilized. No deamination occurred in this time. It is suggested that the metabolic events observed in the simulated system are basically the same as occur in muscle doing heavy work.
...
PMID:Studies with a reconstituted muscle glycolytic system. The anaerobic glycolytic response to simulated tetanic contraction. 427 6

1. The absence of creatine was demonstrated enzymically in the hen's-egg yolk and in the albumin contrary to former reports. 2. A comparison of the results obtained by enzymic and colorimetric methods to measure creatine is presented. 3. Creatine phosphate was not detected in the yolk extracts. 4. The content of free arginine enzymically assayed was 15.7mumol in the yolk and 3.38mumol in the albumin. Arginine amounts to practically all of the guanidine compounds in the yolk and one-half of those in the albumin. 5. No glycine amidinotransferase activity was found in the egg-yolk homogenates. 6. The heart of the chick embryo does not receive creatine from the egg and the creatine kinase activity present in this organ starting from the 27th hour of incubation suggests that the enzyme is a constitutive one working probably as an adenosine triphosphatase in a way similar to the kinase isolated from rabbit skeletal muscle. 7. Liver glycine amidinotransferase activity appeared clearly after day 5 of incubation. The specific activity reached a maximum at day 12 and then declined; however, the activity per total mass of liver increased steadily during all the prenatal period. Concomitantly with this steady increase a rise in the creatine content of the whole embryo was observed. An analogous increasing relationship between total liver amidinotransferase activity and liver creatine content was also detected during the postnatal period. 8. Repression of amidinotransferase by creatine cannot be accepted as occurring under physiological conditions since an inverse relationship between the two parameters was not observed. 9. Repression of liver amidinotransferase is observed only when pharmacological concentrations of the exogenous creatine are present in the chick liver.
...
PMID:Creatine regulation in the embryo and growing chick. 549 9

After 10 wash cycles, 0.8 u.e. of creatine kinase activity remained bound per mg of chicken pectoralis myofibrils which had been freed of soluble creatine kinase, mitochondria, and membranes. The bound creatine kinase is located at the M-band and contributes to the electron density of this sarcomeric structure (Wallimann, T., Pelloni, G.W., Turner, D.C., and Eppenberger, H. M. (1978) Proc. Natl. Acad. Sci. U. S. A. 75, 4296-4300). By measuring the combined actin-activated Mg2+-ATPase and creatine kinase reactions of myofibrils by pH-stat, it was shown that the amount of M-line-bound creatine kinase activity was sufficient to rephosphorylate the ATP hydrolyzed in vitro by the actin-activated Mg2+-ATPase. The amount of M-line-bound creatine kinase and thus the ATP regeneration potential depended on the muscle type. It was higher in fast muscles and lower in slow muscles. Inhibition of myofibrillar creatine kinase or extraction of the M-line-bound enzyme abolished the ATP regeneration potential without affecting ATPase activity. Inhibitors of myokinase, mitochondrial ADP/ATP translocase, and respiration did not affect the ATP regeneration potential or the ATPase. M-line-bound creatine kinase, sufficient to support an ATP turnover rate of 6s-1 per myosin head, seems to have the capacity for the intramyofibrillar regeneration of most or all of the ATP hydrolyzed by the myofibrillar ATPase during muscle contraction. Thus, M-line-bound creatine kinase at the myofibrillar receiving end of the phosphorylcreatine shuttle is of physiological significance.
...
PMID:Function of M-line-bound creatine kinase as intramyofibrillar ATP regenerator at the receiving end of the phosphorylcreatine shuttle in muscle. 614 55

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.
...
PMID:Intracellular energy transport and control of cardiac contraction. 622 78

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.
...
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

Sarcolemmal preparations isolated from rat and guinea pig hearts mostly consisting of inside-out membrane vesicles catalyzed ATP-dependent Ca2+ accumulation. The creatine kinase ATP-regenerating system containing exogenous creatine kinase and phosphocreatine was most effective in supporting Ca2+ accumulation. The normalized rate of Ca2+ accumulation obtained by dividing the Ca2+ uptake rate by its initial equilibrium vesicular content was correlated with the (Na+ K+)-ATPase activity. The ATP-dependent Ca2+ uptake in sarcolemmal vesicles was inhibited by cardenolids--digitoxigenin and ouabain (40-50%), when the latter acted from inside the vesicles. The Ca2+ gradient formed in sarcolemmal vesicles at the expense of ATP was dissipated by Na+ but not by Li+ added into the external medium. The external sodium ions also caused Ca2+ efflux from sarcolemmal vesicles equilibrated with Ca2+. The described effects of Na+ are taken to show the existence of a Na-Ca exchange system in cardiac sarcolemma. Ca2+-ATPase of sarcoplasmic reticulum (SR) vesicles from guinea pig heart as well as ATP-dependent Ca2+ influx in these preparations were found to be partially suppressed by digitoxigenin. External NaCl led to be a rapid (during 5-10 sec) fall in vesicular Ca2+ content (by about 40%) accumulated at the expense of ATP followed by a return of Ca2+ content to its initial level. LiCl had no effect on Ca2+ content in SR. NaCl gradient directed inside the SR vesicles did not influence the distribution of Ca2+ between internal and external vesicular volumes in equilibrium (without ATP). The differences in properties of the Ca-pump of sarcolemma and sarcoplasmic reticulum found in this work support the idea on the existence of sarcolemmal system of ATP-dependent transport of Ca2+.
...
PMID:[Effect of cardenolids and sodium ion gradient on ATP-dependent Ca2+ accumulation in cardiac sarcolemmal vesicles]. 627 79

We have designed and constructed a 25 mm diameter chamber in order to study the phosphorus nuclear magnetic resonance (31P NMR) spectra from a considerable mass of toad and frog muscles (16 sartorii weighing 5-10 g) which were maintained in a well-oxygenated condition at 4 degrees C. We have thus been able to measure the biochemical changes that accompany contraction and recovery with improved time-resolution. Using this apparatus it is shown that splitting of phosphocreatine (PCr) continues for a few minutes after relaxation. Subsequently the PCr is rebuilt by oxidative processes in the familiar way, with a time-constant congruent to 10 min. By studying tetanic contractions of various durations we have shown that the time-course of the post-contractile PCr splitting is similar to that of the heat production that cannot yet be accounted for by known chemical changes. Myosin and actomyosin ATPase reactions most likely underlie the post-contractile ATP utilization. The results suggest that the post-contractile ATP utilization is responsible for the unexplained enthalpy mentioned above.
...
PMID:Post-contractile phosphocreatine splitting in muscle as revealed by time-resolved 31P nuclear magnetic resonance. 642 43

An in vitro rat muscle preparation is described that can contract at rates of 12-240 twitches/min. Maximum dF/dt paralleled maximum twitch tension, their ratio being constant at approximately 8 ms for contraction rates of 12-120 twitches/min. Time to peak tension was 8-13 ms, time to peak dF/dt 5-8 ms, and half-relaxation time 4 ms. These parameters were unaffected by rate of contraction or duration of isometric work. Differential ATPase staining demonstrated that 60-65% of the fibers were fast-twitch white, 20% fast-twitch red, and 15% slow-twitch red. The preponderance of fast-twitch fibers correlated with the observed mechanical performance of the muscle. Muscles contracting for 60 min at rates up to 48 twitches/min maintained total adenine nucleotide content (ATP, ADP, AMP) at near resting levels. At higher twitch rates (72-240 twitches/min), total adenine nucleotide content decreased 40%, reflecting exclusively a fall in ATP in the presence of adequate phosphocreatine stores. Adequate oxygenation was reflected by lactate-to-pyruvate ratios in the range of 11-15 at all rates of contraction.
...
PMID:Epitrochlearis muscle. I. Mechanical performance, energetics, and fiber composition. 644 76

A method is described, based on the differential accumulation of Rb+ and methyltriphenylphosphonium, for the simultaneous estimation of the membrane potentials across the plasma membrane of isolated nerve endings (synaptosomes), and across the inner membrane of mitochondria within the synaptosomal cytoplasm. These determinations, together with measurements of respiratory rates, and ATP and phosphocreatine concentrations, are used to define the bioenergetic behaviour of isolated synaptosomes under a variety of conditions. Under control conditions, in the presence of glucose, the plasma and mitochondrial membrane potentials are respectively 45 and 148mV. Addition of a proton translocator induces a 5-fold increase in respiration, and abolishes the mitochondrial membrane potential. The addition of rotenone to inhibit respiration does not affect the plasma membrane potential, and only lowers the mitochondrial membrane potential to 128mV. Evidence is presented that ATP synthesis by anaerobic glycolysis is sufficient under these conditions to maintain ATP-dependent processes, including the reversal of the mitochondrial ATP synthetase. Addition of oligomycin under non-respiring conditions leads to a complete collapse of the mitochondrial potential. Even under control conditions the plasma membrane (Na+ + K+)-dependent ATPase is responsible for a significant proportion of the synaptosomal ATP turnover. Veratridine greatly increases respiration, and depolarizes the plasma membrane, but only slightly lowers the mitochondrial membrane potential. High K+ and ouabain also lower the plasma membrane potential without decreasing the mitochondrial membrane potential. In non-respiring synaptosomes, anaerobic glycolysis is incapable of maintaining cytosolic ATP during the increased turnover induced by veratridine, and the mitochondrial membrane potential collapses. It is concluded that the internal mitochondria must be considered in any study of synaptosomal transport.
...
PMID:Energy transduction in intact synaptosomes. Influence of plasma-membrane depolarization on the respiration and membrane potential of internal mitochondria determined in situ. 737 8


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---