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:3.6.3.14 (ATP synthase)
7,042 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The immediate and direct regulation of insulin release by circulating nutrients, especially glucose, is thought to be mediated in the pancreatic B-cell by a sequence of metabolic, ionic, and motile events. On the basis of previous work, it is assumed that the process by which glucose is recognized as an insulinotropic agent entirely depends on the metabolic changes evoked by the sugar in the islet cells. Several factors are considered as possible candidates for the coupling between these metabolic changes and subsequent ionic events such as altered phosphate, chloride, sodium, potassium, and calcium handling. It is acknowledged that changes in the concentrations of glycolytic intermediates and cyclic nucleotides (adenosine- or guanosine-3', 5'-cyclic monophosphate), or both, could play a modulatory role upon stimulated insulin release. However, the initiation of insulin release seems to depend on the generation of two essential coupling factors: H+ and reduced pyridine nucleotides. The changes in H+ fluxes may account for the glucose-induced decrease in K+ and Ca2+ fractional outflow rate, all three parameters displaying hyperbolic-like dose-response curves with half-maximal values at noninsulinotropic glucose concentrations. The changes in NAD(P)H concentration may account for a glucose-induced Ca2+--Ca2+ exchange process due to a change in affinity of a native ionophoretic system. The dose-response curves for these parameters yield a sigmoidal pattern analogous to that which depicts the rate of insulin release at increasing glucose concentrations. It is proposed that such a coupling between metabolic and cationic events is operative in response to other insulinotropic nutrients and that its time course may be relevant to the phasic aspect of insulin release. Thus, the nutrient-induced release of insulin (and possibly other pancreatic hormones), which is essential for the regulation of fuel homeostasis, would depend on the capacity of circulating nutrients to act as a fuel in the islet cells. This concept raises a question as to the existence and nature of feedback mechanisms regulating the metabolic fluxes in the islet cells as a function of their energy expenditure.
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PMID:Insulin release: the fuel hypothesis. 3 43

Mammalian and avian muscles were examined histochemically and biochemically to determine the relative contribution of membrane bound (mitochondrial and sarcotubular) ATPases under the same conditions employed for myofibrillar ATPase. For histochemically investigated Ca+(+)-ATPase activity following incubation at pH 9.4 according to the calcium-citro-phosphate technique, avian muscle displayed distinct mitochondrial localization in both dark and light staining fibres. However, mitochondrial localization did not occur in mammalian muscle fibres. Pretreatment of unfixed frozen sections with ouabain, cyanide and acetone did not prevent the reticular distribution in avian muscle fibres. The present study demonstrates that "myofibrillar" localization is achieved by the Ca+(+)-precipitation technique: provided frozen sections are pretreated with cold acetone, fixed in a fixative containing oligomycin or azide and then incubated in a medium containing glycine-NaO H as buffer. Mitochondria prepared by successive mechanical homogenization or by Nagarse treatment plus 2 min homogenization develop different ATPase activities at pH 9.4 7.4 6.0 and 4.35 as well as stimulation by 70 mM Ca++ at these pHs compared to those ATPase activities in the homogenate of mixed hamster hind leg muscles. Glycerol-3-phosphate dehydrogenase and creatine kinase (both located at the outer surface of the inner mitochondrial membrane) and succinate dehydrogenase and glutamate dehydrogenase (localized at the inner mitochondrial membrane and in the matrix resp.) also show different activities in both mitochondria preparations indicating different membrane properties of both mitochondria. Evidence is obtained that using the calcium-citro-phosphate technique at pH 9.4 oligomycin-sensitive and -insensitive ATPases are activated by Ca++ in both mitochondria preparations. Since in muscle homogenate less than 10% of Ca+(+)-stimulated ATPase activity is oligomycin-sensitive, mitochondrial ATPase exhibit only a small portion of total ATPase from mixed hamster hind leg muscles.
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PMID:Histochemical and biochemical investigations of adenosine triphosphatase in vertebrate mixed muscles. 4 33

Effect of respiration toxins is studied on some properties of mitochondrial membranes and functions connected with ion transport for the expence of ATP energy. The combination of three respiration inhibitors (cyanide, antimycin and rotenone) was shown to develope the following effects: 1) the inhibition of K+ accumulation by mitochondria at the presence of ATP and valinomycin; 2) the decrease in acidification of non-mitochondrial space, accompanying to the K+ transport; 3) the activation of latent mitochondrial ATPase; 4) the inhibition of DNP-stimulated ATPase; 5) the inhibition of mitochondria swelling, caused by K+, Ca2+, or dimethyldibenzylammonium (DDA+) at the presence of ATP+phopshate (or acetate); 6) the stimulation of passive mitochondria swelling in 0.1 MNH4NO3; 7) the inhibition of ATP-induced contraction of mitochondria, swelling in NH4NO3. The data obtained are discussed in a wiev of the conception, which suggests that the attaching of inhibitors to respiration enzymes changes the configuration of the latters, thus disturbing natural structural bond of these enzymes with other protein components of the membrane. The latter can result in the impair of electroisolating membrane properties, in the increase of its conductivity for H+ and other ions, and in the decrease of Vm values of some enzymatic reaction, which are not directly connected with the respiration chain (such as ATPase reaction).
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PMID:[Respiration toxins as inhibitors of ion transport, supported by ATP hydrolysis, in mitochondria]. 12 71

A bean chloroplast coupling factor (CF1) with latent Ca2+-dependent ATPase activity was studied. Immunodiffusion of bean (Phaseolus vulgaris) chloroplast and etioplast coupling factors and spinach coupling factor against antiserum to spinach coupling factor showed partial identity of the bean coupling factor with that of spinach. An immunoelectrophoretic comparison, under dissociating conditions, of bean leaf extracts and spinach extracts containing CF1 subunits (as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis) gave identical results for both extracts. At least six distinct polypeptide species were found. The major species had molecular weights of 42 000, 59 000 and 63 000 daltons. Amino acid analysis of electrophoretically purified bean CF1 gave results similar to those published for spinach CF1.
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PMID:Subunit studies of coupling factor 1 of bean chloroplasts. 13 66

Preparation of surface membranes from mouse L-cells using a technique previously described in the literature [Perdue & Sneider, 1970] allowed characterization of a Ca-activated ATPase apparently separate from the mitochondrial ATPase also dependent on calcium. This enzyme is associated with the Na-K-ATPase, a marker for surface membranes, and not wilth alkaline phosphatase, a mitochondrial enzyme. In temperature sensitivity, pH dependence and inhibition by ethacrynic acid, the partially purified enzyme has properties similar to those previously described for active calcium efflux from these cells. For maximal activity of the enzyme system magnesium and sodium are required, although the calcium transport from whole cells was apparently independent of both. Adenosine triphosphate only was metabolized by the enzyme system, whereas CTP could be utilized for calcium transport from 'ghost' cells, probably as a result of intracellular conversion to ATP. It is suggested that the active calcium transport from cultured L-cells is closely linked to the calcium dependent ATPase, and that the method of calcium extrusion is similar to that described for red blood cells.
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PMID:Properties of the calcium-activated adenosine tri-phosphatase from L-cell membranes. 13 77

The effects of tentoxin on the ATPase activities of coupling factor 1 proteins (CF1) and photophosphorylation with isolated chloroplasts and chloroplasts reconstituted with coupling factor proteins have been examined. 1. The calcium-dependent ATPase activities of coupling factors isolated from spinach, lettuce and Nicotiana otophora are completely inhibited by tentoxin. The ATPase activities of coupling factors isolated from Nicotiana tabacum and Nicotiana knightiana are not affected by tentoxin. 2. Phenazine methosulfate-catalyzed cyclic photophosphorylation with chloroplasts isolated from spinach, lettuce and N. otophora is completely inhibited by tentoxin, whereas chloroplasts isolated from N. knightiana and N. tabacum are relatively insensitive to tentoxin. 3. Spinach chloroplasts, partially depleted in CF1, can be reconstituted with coupling factors isolated from a wide variety of plants including lettuce, radish, N. tabacum, N. knightiana and N. otophora. 4. Spinach chloroplasts reconstituted with spinach, lettuce and N. otophora CF1 retain their sensitivity to tentoxin; however, when reconstituted with N. knightiana and N. tabacum coupling factor proteins, a significant fraction of the reconstituted rate remains tentoxin insensitive. These data are interpreted as evidence that coupling factors that reconstitute with spinach thylakoid membranes have both a catalytic and structural function.
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PMID:Evidence for a catalytic function of the coupling factor 1 protein reconstituted with chloroplast thylakoid membranes. 14 3

The membrane ATPase (EC 3.6.1.3) of Bacillus subtilis can be solubilized by a shock-wash process. Two procedures for purifying the solubilized enzyme are reported. A protease inhibitor, phenylmethane sulfonylfluoride, was introduced in the solubilization and purification step. The resultant ATPase purified by density gradient centrifugation has a molecular weight of 315 000, an s20,w of 13,4 and an amino acid composition very similar to bacterial ATPases already studied. After exposure to polyacrylamide gel electrophoresis in presence of sodium dodecyl sulphate (SDS), or 8 M urea or SDS-urea, the purified ATPase can be dissociated in two non-identical subunits of molecular weights 59 000 (alpha) and 57 000 (beta) with different charges. Kinetic studies showed that Ca2+ or Zn2+ are required for ATPase activity, although Mg2+ was uneffective. At optimal Ca2+ concentration, the Mg2+ has an inhibitory effect. The Km for ATP is 1.3 mM. Inhibitors of the oxydative phosphorylation, of the mitochondrial ATPase and of the (Na+ + K+)-ATPase are studied.
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PMID:Membrane ATPase of Bacillus subtilis. I. Purification and properties. 14 10

1. The distribution of ATPase and several marker enzymes was examined after differential and sucrose gradient centrifugation of yeast homogenates. 2. An ATPase activity not sensitive to oligomycin is found exclusively associated with a particulate fraction equilibrating at densities of 1.23-1.25. This particulate material shows the chemical and enzymatic characteristics of the yeast plasma membrane. 3. The pH optimum of the plasma membrane ATPase is 5.6, as compared with 8.5 for the mitochondrial ATPase. In addition to oligomycin, the enzyme is not sensitive to other inhibitors of the mitochondrial ATPase as azide, dicyclohexylcarbodiimide and the mitochondrial ATPase inhibitor protein. It is inhibited by p-chloromercuryphenyl sulfonate, fluoride, quercetin and by the antibiotic Dio-9 but is not affected by ouabain. 4. The plasma membrane ATPase shows a high affinity for ATP (Km = 0.1 mM) and is very specific for this compound, hydrolyzing other nucleotide triphosphates less than 25% as rapidly. No activity was detected with ADP. 5. The enzyme requires a divalent cation for activity and Mg2+ is the most effective. It is not significantly stimulated by K+ or bicarbonate and Ca2+ is inhibitory. 6. The activity cannot be assayed in intact cells unless they are permeabilized with toluene. This suggest that the active site is on the cytoplasmic side of the plasma membrane.
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PMID:Characterization of the plasma membrane ATPase of Saccharomyces cerevisiae. 15 59

The enzymic activity of Mg2+- or Ca2+-stimulated ATPase from Escherichia coli was inhibited by one of the troponin components, TN-I, and by mitochondrial ATPase inhibitor (F1-inhibitor). The inhibitory ability of component TN-I against Mg2+-stimulated AtPase activity was lost after digestion of component TN-I with trypsin. The Mg2+-stimulated ATPase activity inhibited by component TN-I was completely restored by the addition of another troponin component TN-C.
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PMID:Inhibition of E coli ATPase activity by a troponin component, TN-I, and by mitochondrial ATPase inhibitor. 16 Mar 25

The effect of thyroxine administration upon ATPase activity of several subcellular fractions of livers from rats and guinea pigs has been studied. To determine a patho-physiological dose of levo thyroxine [T4] for guinea pigs, a dose-response curve was examined of T4 effect upon oxidative phosphorylatin of guinea pig liver mitochondria. Maximum stimulation of mitochondrial respiration without uncoupling of oxidative phosphorylation was found with 15 microgram of T4 per 100 g body weight per day. This dose of T4 stimulated Mg++ activated ATPase of plasma membranes of guinea pigs and slightly stimulated Mg++ activated ATPase of guinea pig liver nuclear membranes. Rat liver nuclear membrane ATPase was not responsive to thyroxine at doses from 5 to 150 microgram per 100 g body weight. T4 significantly stimulated Ca++ or Mg++ ATPase of mitochondria and microsomes from both rat and guinea pig liver. Microsomes from both species were maximally activated by Mg++ and no significant additional stimulation with Ca++ was found. Mitochondrial ATPase from both species showed significantly greater Ca++ plus Mg++ ATPase activity than did Mg++ alone. Ca++ activated ATPase was approximately equal to dinitrophenol stimulated mitochondrial ATPase. Maximum activation of microsomal ATPase in both species was found with 1 mM calcium. We conclude that at physiological-intracellular concentrations of Ca++ and Mg++, thyroxine probably stimulates Mg++ activated microsomal ATPase and Ca++ activated mitochondrial ATPase. A potential role of Ca++ as a moderator of thyroxine stimulated activity in mitochondria and the relation of calcium to other metabolic reactions that are thyroxine sensitive is discussed.
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PMID:L-Thyroxine effects upon ATPase activities of several subcellular fractions of liver of the rat and the guinea pig. 16 Sep 23


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