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)

The pancreas is a 'leaky' epithelium and secretes a juice in which sodium and potassium have concentrations similar to those of plasma. The characteristic features of the secretion are its isosmolality and its high bicarbonate concentration. It is the latter that has attracted considerable attention. Secretion in the isolated cat pancreas is directly proportional to the bicarbonate concentration in the nutrient fluid. The ability of the gland to secrete weak acids has led to the view that because of the very different chemical nature of the anions, it is most likely that it is a component common to all buffers, the proton, that is subject to active transport. This is supported by the decrease in pH and the increase in rho CO2 of the venous effluent when secretion occurs and the sensitivity of secretion to the pH of the nutritional extracellular fluid. It is proposed that the cellular mechanisms are as follows: CO2 diffuses into the cell and is hydrated to carbonic acid under the influence of carbonic anhydrase. The bicarbonate ion so formed diffused into the ductular lumen and the proton is transported backwards through the epithelium with a proton pump (Mg2+ -ATPase) provisionally located in the luminal membrane and a hydrogen-sodium exchange carrier located in the basolateral membrane. Energy for the latter process is derived from the sodium gradient between extracellular fluid and cell. This gradient is maintained by a (Na+ + K+)-ATPase also located in the basolateral membrane. Chloride appears to be transported partly through a chloride-bicarbonate exchange mechanism but largely passively together with a large sodium and potassium component through the paracellular pathway. Osmotic equilibrium is likely to occur in the small ductules.
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PMID:Ionic transport mechanisms underlying fluid secretion by the pancreas. 612 41

Isolated spontaneously beating rat hearts were perfused in the Langendorff mode and divided into four groups, i.e., control (aerobic), hypoxic (95% N2-5% CO2), ischemic, and ischemic reperfused. After a total of 90 min of perfusion, the sarcolemma was isolated and enzymatically characterized. Ouabain-sensitive Na+-K+-ATPase was inhibited in all three experimental groups, whereas K+-stimulated phosphatase activity was decreased only in the ischemic and reperfused groups compared with control. 5'-Nucleotidase activity was inhibited (P less than 0.05) only in the ischemic group. Mg2+-ATPase activity was not different from control. Passive Ca2+ uptake and Ca2+ efflux were not significantly altered by any of the interventions. Na+-Ca2+ exchange rate, but not capacity, was decreased (by 32-42%) in the ischemic group but this was partially reversed on reperfusion. These results suggest that changes secondary to lack of flow rather than O2 play a major role in the etiology of ischemic damage to the membrane and that a 15-min period of reperfusion after 60 min of ischemia does not exacerbate this damage.
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PMID:Sarcolemmal enzymes and Na+ -Ca2+ exchange in hypoxic, ischemic, and reperfused rat hearts. 614 98

Much evidence shows that glia regulates the cation and anion content of brain interstitial space. In rats the pH and bicarbonate (HCO3-) concentration of neurons and glia were derived from carbon 14-labeled HCO3- and dimethyloxazolidinedione uptake into brain and cerebrospinal fluid. Acetazolamide increases the total CO2 concentration in neurons and decreases the pH and HCO3- concentration in glia. Inhibition of glial carbonic anhydrase (CA) reduces conversion of neuronally derived CO2 to HCO3-, glial pH is lowered, and neuronal CO2 accumulates. CA therefore has an essential role in regulating pH in neurons, glia, and interstitial fluid. In audiogenic seizure mice, glial CA activity is increased and glial anion transport is reduced. As the mice age, seizure susceptibility, the increased CA activity, and the defect in anion transport disappear concurrently. The enhanced CA activity in the glial cells of these mice is an adaptive mechanism to overcome the defect in anion transport that results from a deficiency of HCO3- -dependent and Na+- and K+ -dependent adenosine triphosphatase. Pentylenetetrazol stimulates neurons in neonatal rats, but after 10 days of age, when glia is present, it too is stimulated and the seizures are attenuated. Cobalt implantation in the cortex of rats also induces a glial response that ameliorates the focal seizures produced by this procedure.
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PMID:Ionic and acid-base regulation of neurons and glia during seizures. 615 Jun 82

Mucosal homogenates from rat jejunum were tested for both HCO-3-stimulated ATPase and anion-stimulated, SCN-inhibited ATPase in assay mixtures ungassed, gassed with pure oxygen or gassed with the appropriate gaseous phase. Experiments were performed at four different initial pHs (7.15; 7.45; 8.10; 8.55) with or without the presence of Triton X-100. Assay mixtures were tested for both pH and % CO2. Only at pH 7.15 and 7.45 anion-sensitive ATPase activities in ungassed conditions are different from those in mixtures gassed with the proper gaseous phase. Moreover, at cited pHs in ungassed mixtures the final pH is higher and % CO2 is lower than initial values. Therefore it seems possible to obtain the exact determination of anion-sensitive ATPases at all pH values only from mixtures gassed with the proper gaseous phase. Bicarbonate-stimulated ATPase activity is absent both at pH 7.15 and 7.45; this fact seems to exclude, at these pHs, an active transport of bicarbonate directly depending on this enzyme activity.
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PMID:ph-dependent, HCO-3-stimulated ATPase of rat jejunum. 618 53

In urinary epithelia, like the turtle bladder, protons are transported by a H+ translocating ATPase located in the luminal membrane. We have recently discovered that the H+ pump is stored in small vesicles that lie underneath the luminal membrane. CO2, a major regulator of H+ transport causes these vesicles to fuse with the membrane thereby inserting more H+ pumps. We have now isolated these vesicles from the turtle bladder and from beef kidney medulla. Based on inhibitor sensitivity and substrate specificity this proton translocating ATPase is different from the mitochondrial F0-F1 ATPase, yeast plasma membrane and the gastric H+,K+-ATPase. Solubilization and reconstitution of the enzyme into liposomes shows retention of transport activity and inhibitor sensitivity.
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PMID:Regulation of proton transport in urinary epithelia. 619 5

The localization of carbonic anhydrase (CA) was studied in rat skeletal muscles with the use of immunohistochemical (peroxidase-antiperoxidase) method. CA was observed in all those fibers that also showed pH 4.3 stable actomyosin adenosine triphosphatase activity (type I fibers), but the reverse did not necessarily hold. More specifically, CA was apparently localized in I-bands, and a weak reaction was also observed in sarcolemma. The function of CA in muscle fibers is possibly connected with the greater demands on CO2 transport and buffer system in muscles adapted to long-lasting contractions.
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PMID:Carbonic anhydrase in the type I skeletal muscle fibers of the rat. An immunohistochemical study. 621 80

The reduction of CO2 or any other methanogenic substrate to methane serves the same function as the reduction of oxygen, nitrate or sulfate to more reduced products. These exergonic reactions are coupled to the production of usable energy generated through a charge separation and a protonmotive-force-driven ATPase. For the understanding of how methanogens derive energy from C-1 unit reduction one must study the biochemistry of the chemical reactions involved and how these are coupled to the production of a charge separation and subsequent electron transport phosphorylation. Data on methanogenesis by a variety of organisms indicates ubiquitous use of CH3-S-CoM as the final electron acceptor in the production of methane through the methyl CoM reductase and of 5-deazaflavin as a primary source of reducing equivalents. Three known enzymes serve as catalysts in the production of reduced 5-deazaflavin: hydrogenase, formate dehydrogenase and CO dehydrogenase. All three are potential candidates for proton pumps. In the organisms that must oxidize some of their substrate to obtain electrons for the reduction of another portion of the substrate to methane (e.g., those using formate, methanol or acetate), the latter two enzymes may operate in the oxidizing direction. CO2 is the most frequent substrate for methanogenesis but is the only substrate that obligately requires the presence of H2 and hydrogenase. Growth on methanol requires a B12-containing methanol-CoM methyl transferase and does not necessarily need any other methanogenic enzymes besides the methyl-CoM reductase system when hydrogenase is present. When bacteria grow on methanol alone it is not yet clear if they get their reducing equivalents from a reversal of methanogenic enzymes, thus oxidizing methyl groups to CO2. An alternative (since these and acetate-catabolizing methanogens possess cytochrome b) is electron transport and possible proton pumping via a cytochrome-containing electron transport chain. Several of the actual components of the methanogenic pathway from CO2 have been characterized. Methanofuran is apparently the first carbon-carrying cofactor in the pathway, forming carboxy-methanofuran. Formyl-FAF or formyl-methanopterin (YFC, a very rapidly labelled compound during 14C pulse labeling) has been implicated as an obligate intermediate in methanogenesis, since methanopterin or FAF is an essential component of the carbon dioxide reducing factor in dialyzed extract methanogenesis. FAF also carries the carbon at the methylene and methyl oxidation levels.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The bioenergetics of methanogenesis. 623 47

The content of adenine nucleotides, ATPase activity, the amount of total and inorganic phosphorus in the carp liver mitochondria were studied as affected by CO2 high concentrations. It is shown that during adaptation to the CO2 higher level in the medium the amount of ATP in fishes undergoes the most significant changes. The organism response to the effect of carbon dioxide depends on its concentration in the medium and time of its action. When fishes were for 24h under conditions of the 0.4mM CO2 concentration, the ATP content in the carp liver mitochondria surpasses the control level and under conditions the 0.8 mM CO2 concentration it reaches the control level. The presence of 0.4 and 0.8 mM CO2 concentration decreases the ATP content 7 days later. The amount of inorganic phosphorus in the liver mitochondria of experimental fishes undergoes similar changes. An increase in the CO2 concentration in the water medium up to 0,4 and 0,8 mM inhibits Na+, K+, Mg2+-ATPase in fish organelles, the inhibition being more pronounced in a trial with 0.8 mM CO2.
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PMID:[Peculiarities of phosphoric compound metabolism in liver mitochondria of carp adapted to higher concentrations of CO2 in water]. 624 95

The coupling between H+ transport (JH) and anaerobic glycolysis was examined in vitro in an anaerobic preparation of turtle urinary bladder. JH was measured as the short-circuit current after Na+ transport was abolished with ouabain and by pH stat titration. The media were gassed with N2 and 1% CO2 (PO2 less than 0.5 mm Hg) and contained 10 mM glucose. Under these conditions, JH was not inhibited by 3 mM serosal (S) cyanide or by 0.1 mM mucosal (M) dinitrophenol. Control anaerobic lactate production (Jlac) of 47 bladders was plotted as a function of simultaneously measured JH. The slope of Jlac on JH was 0.58 0.12 with an intercept for Jlac at JH = 0 of 0.55 micromol/hr. Values for delta Jlac/delta JH were determined in groups of individual bladders when JH was inhibited by an opposing pH gradient (0.55 0.16), by acetazolamide (0.58 0.19) and by dicyclohexylcarbodiimide, DCCD (0.58 0.14). The constancy of delto Jlac/ delta JH indicates a high degree of coupling between JH and Jlac. Since the anaerobic metabolism of glucose produces one ATP for each lactate formed, the delta Jlac/ delta JH values can be used to estimate the stoichiometry of H+ translocation. The movement of slightly less than 2H+ ions is coupled to the hydrolysis of one ATP. During anaerobiosis (absence of mitochondrial ATPase function) the acidification pump was not inhibited by M addition of oligomycin but was inhibited by M addition of DCCD and Dio-9, inhibitors of H+ flow in the proteolipid portion of H+-translocating ATPases. DCCD inhibited anaerobic JH without change in delta Jlac/delta JH or basal Jlac and, therefore, acted primarily on the H+ pump. S addition of vanadate also inhibited JH, but the inhibition was associated with an increase in Jlac. The site of this apparent uncoupling remains to be defined. The acidification pump of the luminal cell membrane of the turtle bladder has H+-ATPase characteristics that differ from mitochondrial ATPase in that H+ transport is oligomycin-resistant and vanadate-sensitive. As judged from the flows of H+ and lactate, the H+/ATP stoichiometry of the pump is about 2.
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PMID:Coupling between H+ transport and anaerobic glycolysis in turtle urinary bladder: effect of inhibitors of H+ ATPase. 626 81

The effect of removal of peritubular protein on the reabsorption of various solutes and water was examined in isolated rabbit proximal convoluted tubules (PCT) perfused in vitro. In 22 PCT perfused with ultrafiltrate (UF) and bathed in serum, volume absorption (Jv) was 1.44 nl/mm per min and potential difference (PD) was -3.6 mV. When these same PCT were bathed in a protein-free UF, Jv was reduced 38% without a change in PD. Simultaneous measurements of total CO2 net flux (JTCO2) and glucose efflux (JG) showed that less than 2% of the decrease in JV could be accounted for by a reduction in JTCO2 and JG, suggesting that removal of peritubular protein inhibited sodium chloride transport (JNaCl). Therefore, in eight additional PCT, JNaCl was measured, in addition to PD, Jv, JG, and JTCO2. In these PCT, the decrease in total solute transport induced by removal of bath protein was 201.7 +/- 37.5 posmol/mm per min. JG decreased slightly (9.1 +/- 3.9 posmol/mm per min); NaHCO3 transport did not change (9.2 +/- 6.6 posmol/mm per min); but JNaCl decreased markedly (160.6 +/- 35.7 posmol/mm per min). 80% of the decrease in Jv could be accounted for by a decrease in JNaCl. In 13 additional PCT perfused with simple NaCl solutions, a comparable decrease in Jv and JNaCl was observed when peritubular protein was removed without an increase in TCO2 backleak. In summary, removal of peritubular protein reduced Jv and JNacl, but did not significantly alter PD, JG, JTCO2, or TCO2 backleak. The failure to inhibit JG and JTCO2, known sodium-coupled transport processes, indicates that protein removal does not primarily affect the Na-K ATPase pump system. Furthermore, since PD and TCO2 backleak were not influenced, it is unlikely that protein removal increased the permeability of the paracellular pathway. We conclude that protein removal specifically inhibits active transcellular or passive paracellular NaCl transport.
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PMID:Influence of peritubular protein on solute absorption in the rabbit proximal tubule. A specific effect on NaCl transport. 626 6


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