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1.
The relationship between the (Na(+) and K(+))-activated adenosine triphosphatase enzyme system implicated in sodium-transport by cell membranes and the calcium-activated adenosine triphosphatase, which is generally associated with calcium uptake, was examined in microsomes from skeletal muscle. Whereas sodium and potassium did not modify the relatively low adenosine triphosphatase activity seen in the absence of calcium, a pattern similar to that of the sodium-transport enzyme system was seen afer the addition of CaCl(2). The calcium-activated adenosine triphosphatase was stimulated equally by sodium or potassium alone, but both the rate and extent of calcium uptake were enhanced more by potassium than by sodium at concentrations below 0.12 mole per liter. In the absence of either of these ions addition of calcium failed to activate adenosine triphosphatase although significant amounts of calcium were taken up by the microsomes. 相似文献
2.
Muscle contraction and free energy transduction in biological systems 总被引：52，自引：0，他引：52
Muscle contraction occurs when the actin and myosin filaments in muscle are driven past each other by a cyclic interaction of adenosine triphosphate (ATP) and actin with cross-bridges that extend from myosin. Current biochemical studies suggest that, during each adenosine triphosphatase cycle, the myosin cross-bridge alternates between two main conformations, which differ markedly in their strength of binding to actin and in their overall structure. Binding of ATP to the cross-bridge induces the weak-binding conformation, whereas inorganic phosphate release returns the cross-bridge to the strong-binding conformation. This cross-bridge cycle is similar to the kinetic cycle that drives active transport and illustrates the general principles of free energy transduction by adenosine triphosphatase systems. 相似文献
3.
Mercurial-induced transformation of myosin prevented by adenosine triphosphate and pyrophosphate 总被引：1，自引：0，他引：1
D R Kominz 《Science (New York, N.Y.)》1965,149(690):1374-1375
Adenosine triphosphate and pyrophosphate prevent the loss of Ca(//)-activated adenosine triphosphatase activity caused by high concentrations of mercurial sulfhydryl reagent. They concomitantly prevent the transformation of myosin into faster-sedimenting products. This is adduced as support for the hypothesis that the strategic sulfhydryl group is not binding adenosine triphosphate at the active site, but is initiating a conformational change upon its reaction with the mercurial reagent. 相似文献
4.
Actin-myosin interaction: inhibition of the myosin adenosine triphosphatase by actin 总被引：1，自引：0，他引：1
In the absence of magnesium ion, the addition of actin to myosin in a 1 :4 ratio has a strong inhibitory effect on the adenosine triphosphatase activity, in contrast to the well-known activating effect of actin in the presence of magnesium ion. This finding suggests that both effects result from a conformational change in the active site of the myosin adenosine triphosphatase. 相似文献
5.
Adenosine triphosphate usage by flagella 总被引：5，自引：0，他引：5
C J Brokaw 《Science (New York, N.Y.)》1967,156(771):76-78
Comparison of beat frequencies with rates of dephosphorylation of adenosine triphosphate by glycerinated sea urchin spermatozoa as functions of adenosine triphosphate concentration suggests that each molecule of the flagellar adenosine triphosphatase, dynein, dephosphorylates one adenosine triphosphate molecule during each beat cycle. 相似文献
6.
Intestinal calcium transport: the role of sodium 总被引：7，自引：0，他引：7
The role of sodium in intestinal calcium transport was investigated in everted rat intestine. Ethacrynic acid, but not ouabain, inhibited calcium transport. However, ouabain did inhibit net water transport and, therefore, sodium transport, establishing the dissociation of the two transport processes. In addition to a magnesium-dependent adenosine triphosphatase (activated by sodium and potassium), a phosphatase dependent on sodium and calcium was localized to the lateral and basal membrane fractions of the mucosal cell. Activity of the latter phosphatase, similar to calcium transport in intact tissue, was inhibited by ethacrynic acid and not by ouabain. Sodium, therefore, may participate in the calcium transport process by activating an enzyme complex, dependent on adenosine triphosphate, that mediates calcium transport. 相似文献
7.
The membrane rotor ring from the vacuolar-type (V-type) sodium ion-pumping adenosine triphosphatase (Na+-ATPase) from Enterococcus hirae consists of 10 NtpK subunits, which are homologs of the 16-kilodalton and 8-kilodalton proteolipids found in other V-ATPases and in F1Fo- or F-ATPases, respectively. Each NtpK subunit has four transmembrane alpha helices, with a sodium ion bound between helices 2 and 4 at a site buried deeply in the membrane that includes the essential residue glutamate-139. This site is probably connected to the membrane surface by two half-channels in subunit NtpI, against which the ring rotates. Symmetry mismatch between the rotor and catalytic domains appears to be an intrinsic feature of both V- and F-ATPases. 相似文献
8.
A tight coupling between adenosine triphosphate (ATP) hydrolysis and vectorial ion transport has to be maintained by ATP-consuming ion pumps. We report two crystal structures of Ca2+-bound sarco(endo)plasmic reticulum Ca2+-adenosine triphosphatase (SERCA) at 2.6 and 2.9 angstrom resolution in complex with (i) a nonhydrolyzable ATP analog [adenosine (beta-gamma methylene)-triphosphate] and (ii) adenosine diphosphate plus aluminum fluoride. SERCA reacts with ATP by an associative mechanism mediated by two Mg2+ ions to form an aspartyl-phosphorylated intermediate state (Ca2-E1 approximately P). The conformational changes that accompany the reaction with ATP pull the transmembrane helices 1 and 2 and close a cytosolic entrance for Ca2+, thereby preventing backflow before Ca2+ is released on the other side of the membrane. 相似文献
9.
ASKARI A 《Science (New York, N.Y.)》1963,141(3575):44-45
5'-Adenylic acid deaminase free from sodium and potassium ion is prepared from erythrocytes by a convenient method. Like adenosine triphosphatase and adenylic kinase from erythrocytes, the deaminase is activated by some monovalent cations, but unlike these enzymes it requires the presence of a monovalent cation. In all three instances the pattern of activation by ions is similar and suggests a common mechanism. 相似文献
10.
Actomyosin-like protein isolated from mammalian brain 总被引：6，自引：0，他引：6
A protein with characteristics similar to actomyosin has been isolated from whole brain of rat and cat. It is soluble in 0.6 molar potassium chloride and insoluble in 0.1 molar potassium chloride. It superprecipitates with magnesium ions and adenosine triphosphate. It has adenosine triphosphatase activity stimulated by either magnesium or calcium ions. Both superprecipitation and adenosine triphosphatase activity are inhibited by p-chloromercuribenzoate and Mersalyl but not by ouabain. 相似文献
11.
Glycerinated muscle fibers: relation between isometric tension and adenosine triphosphate hydrolysis
The isometric tension of glycerinated muscle fibers and the adenosine triphosphatase activity of homogenates were determined as a function of the concentration of adenosine triphosphate without the addition of divalent cations. These two phenomena are not parallel; large tensions can be developed with negligible hydrolysis of adenosine triphosphate. It is concluded that the large negative free energy change of the hydrolysis is not required for shortening or development of tension. 相似文献
12.
Oscillations of cytosolic sodium during calcium oscillations in exocrine acinar cells 总被引：7，自引：0，他引：7
In acinar cells from rat salivary glands, cholinergic agonists cause oscillations in cytoplasmic free calcium concentration, which then drive oscillations of cell volume that reflect oscillating cell solute content and fluid secretion. By quantitative fluorescence ratio microscopy of an intracellular indicator dye for sodium, it has now been shown that large amplitude oscillations of sodium concentration were associated with the calcium and cell volume oscillations. Both calcium and sodium oscillations were dependent on the continued presence of calcium in the extracellular medium and were abolished by the specific sodium-potassium adenosine triphosphatase inhibitor ouabain. Thus, calcium oscillations in salivary acinar cells, by modulating the activities of ion transport pathways in the plasma membrane, can cause significant oscillations of monovalent ions that may in turn feed back to regulate calcium oscillations and fluid secretion. 相似文献
13.
Microtubule gelation-contraction: essential components and relation to slow axonal transport 总被引：8，自引：0，他引：8
R C Weisenberg J Flynn B C Gao S Awodi F Skee S R Goodman B M Riederer 《Science (New York, N.Y.)》1987,238(4830):1119-1122
Preparations of microtubule proteins isolated by assembly and disassembly undergo gelation-contraction after addition of adenosine triphosphate (ATP). A particulate fraction from these preparations that is required, along with purified tubulin, to produce ATP-dependent microtubule gelation-contraction in vitro has been isolated. The particulates exhibited microtubule-stimulated adenosine triphosphatase activity and moved slowly (about 1 micrometer per minute) along microtubule walls in the presence of ATP. The particulates contained tubulin, neurofilament, and spectrin polypeptides. The composition, solubility, and motility of the particulates are consistent with those of slow component a of axonal transport. 相似文献
14.
Taste receptors which evoke ingestion of blood in the mosquito, Aedes aegypti L., are stimulated by adenosine tetraphosphate, adenosine triphosphate, and adenosine monophosphate, in decreasing order. No other nucleotide is effective. Certain chelators can partially simulate the effect of nucleotides. The feeding response is elicited only at an osmotic pressure close to that of blood, and requires the presence of sodium ions. 相似文献
15.
The influx of K+ into swollen mitochondria in the presence of valinomycin results in the synthesis of adenosine triphosphate in which approximately one H+ disappears per adenosine triphosphate synthesized. The synthesis is blocked by atractyloside but is insensitive to oligomycin and relatively insensitive to uncouplers. 相似文献
16.
The crystal structure of the high-affinity Escherichia coli MetNI methionine uptake transporter, a member of the adenosine triphosphate (ATP)-binding cassette (ABC) family, has been solved to 3.7 angstrom resolution. The overall architecture of MetNI reveals two copies of the adenosine triphosphatase (ATPase) MetN in complex with two copies of the transmembrane domain MetI, with the transporter adopting an inward-facing conformation exhibiting widely separated nucleotide binding domains. Each MetI subunit is organized around a core of five transmembrane helices that correspond to a subset of the helices observed in the larger membrane-spanning subunits of the molybdate (ModBC) and maltose (MalFGK) ABC transporters. In addition to the conserved nucleotide binding domain of the ABC family, MetN contains a carboxyl-terminal extension with a ferredoxin-like fold previously assigned to a conserved family of regulatory ligand-binding domains. These domains separate the nucleotide binding domains and would interfere with their association required for ATP binding and hydrolysis. Methionine binds to the dimerized carboxyl-terminal domain and is shown to inhibit ATPase activity. These observations are consistent with an allosteric regulatory mechanism operating at the level of transport activity, where increased intracellular levels of the transported ligand stabilize an inward-facing, ATPase-inactive state of MetNI to inhibit further ligand translocation into the cell. 相似文献
17.
Calmodulin activation of calcium-dependent sodium channels in excised membrane patches of Paramecium 总被引：8，自引：0，他引：8
Calmodulin is a calcium-binding protein that participates in the transduction of calcium signals. The electric phenotypes of calmodulin mutants of Paramecium have suggested that the protein may regulate some calcium-dependent ion channels. Calcium-dependent sodium single channels in excised patches of the plasma membrane from Paramecium were identified, and their activity was shown to decrease after brief exposure to submicromolar concentrations of calcium. Channel activity was restored to these inactivated patches by adding calmodulin that was isolated from Paramecium to the cytoplasmic surface. This restoration of channel activity did not require adenosine triphosphate and therefore, probably resulted from direct binding of calmodulin, either to the sodium channel itself or to a channel regulator that was associated with the patch membrane. 相似文献
18.
Imaging elemental distribution and ion transport in cultured cells with ion microscopy 总被引：2，自引：0，他引：2
Both elemental distribution and ion transport in cultured cells have been imaged by ion microscopy. Morphological and chemical information was obtained with a spatial resolution of approximately 0.5 micron for sodium, potassium, calcium, and magnesium in freeze-fixed, cryofractured, and freeze-dried normal rat kidney cells and Chinese hamster ovary cells. Ion transport was successfully demonstrated by imaging Na+-K+ fluxes after the inhibition of Na+- and K+ -dependent adenosine triphosphatase with ouabain. This method allows measurements of elemental (isotopic) distribution to be related to cell morphology, thereby providing the means for studying ion distribution and ion transport under different physiological, pathological, and toxicological conditions in cell culture systems. 相似文献
19.
The calcium-activated adenosine triphosphatase activity of cultured single beating heart cells of the rat was localized and visualized by incubating the cells, after extraction in a mixture of glycerol and water, with adenosine triphosphate and calcium. The calcium phosphate, precipitated at the site of the enzyme reaction, was converted into a visible precipitate. The enzyme activity appeared in bands perpendicular to the myofibrils. 相似文献
20.
A G protein directly regulates mammalian cardiac calcium channels 总被引：45，自引：0，他引：45
A Yatani J Codina Y Imoto J P Reeves L Birnbaumer A M Brown 《Science (New York, N.Y.)》1987,238(4831):1288-1292
A possible direct effect of guanine nucleotide binding (G) proteins on calcium channels was examined in membrane patches excised from guinea pig cardiac myocytes and bovine cardiac sarcolemmal vesicles incorporated into planar lipid bilayers. The guanosine triphosphate analog, GTP gamma S, prolonged the survival of excised calcium channels independently of the presence of adenosine 3',5'-monophosphate (cAMP), adenosine triphosphate, cAMP-activated protein kinase, and the protein kinase C activator tetradecanoyl phorbol acetate. A specific G protein, activated Gs, or its alpha subunit, purified from the plasma membranes of human erythrocytes, prolonged the survival of excised channels and stimulated the activity of incorporated channels. Thus, in addition to regulating calcium channels indirectly through activation of cytoplasmic kinases, G proteins can regulate calcium channels directly. Since they also directly regulate a subset of potassium channels, G proteins are now known to directly gate two classes of membrane ion channels. 相似文献