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)

Facilitated diffusion of [14C]lactose into inverted membrane vesicles of Escherichia coli was measured using HgCl2 as a stopping reagent and polylysine to flocculate the vesicles for filtration. Equilibration of lactose between the internal and external volumes required expression of the y gene of the lac operon and was inhibited by thiodigalactoside or by prior incubation with N-ethylmaleimde or HgCl2. The initial rate of uptake was saturable, with a Kt of 0.95 mM. Counterflow of [14C]lactose was demonstrated in either direction. ATP hydrolysis or respiration drove the efflux of internal lactose. The effect of ATP required addition of F1 coupling factor (ATPase) from E. coli when lactose transport was studied in F1-deficient inverted vesicles. Accumulation of lactose against a concentration gradient was achieved by forming an artificial electrochemical proton gradient consisting of a membrane potential negative inside or a pH gradient basic inside. Addition of ATP inhibited this proton driven uptake showing that it occurred in inverted vesicles. It was concluded that the lactose-proton co-transport protein (M protein) is qualitatively symmetrical with respect to the facilitated diffusion of lactose and the coupling of proton and lactose transport.
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PMID:Studies of the beta-galactoside transporter in inverted membrane vesicles of Escherichia coli. I. Symmetrical facilitated diffusion and proton gradient-coupled transport. 2 Nov 83

Sarcoplasmic reticulum (SR), Ca2+ plus Mg2+-ATPase, and Ca2+-ionophore were obtained from white rabbit skeletal muscles. Methylmercury inhibited the Ca2+ plus Mg2+-ATPase and Ca2+-transport but had no effect on the Ca2+-ionophore. Mercuric chloride inhibited all three functions (i.e., ATPase, transport and ionophoric activity). The mechanism of HgCl2 inhibition of the Ca2+-ionophore was by competition with Ca2+ for Ca2+-ionophoric site whereas its inhibition of the enzyme and Ca2+-transport was due to the blockage of essential sulfhydryl (--SH) groups. Ca2+ plus Mg2+-ATPase and Ca2+-transport were more sensitive to methylmercury than to HgCl2. Acetylcholine receptor (AChR) was obtained for the electric organ of T. californica. Methylmercury inhibited the ACh binding to AChR WITH Ki = 5.7 - 10(-6) M. This effect was not due to mercuric ion alone since mercuric chloride up to 10(-4) M did not affect ACh binding to AChR. It is concluded that: the Ca2+ plus Mg2+-ATPase and Ca2+-transport contain --SH groups essential for their activity, and that the two functions are tightly coupled; the Ca2+-ionophore contains no --SH groups essential for its activity; CH3HgCl inhibition of Ca2+ plus Mg2+-ATPase and Ca2+-transport is partly due to its reactivity with --SH groups in hydrophobic environment; the Ca2+-transport is inhibited by HgCl2 through two processes, one which is the blockage of --SH groups and another which is the inhibition of the Ca2+-ionophoric site; and the inhibition of ACh binding to AChR is due to the blockage of --SH groups in hydrophobic environment, which is inaccessible to Hg2+. Our data present for the first time a molecular basis for the myopathy associated with mercurial compounds toxicity.
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PMID:Differential effects of mercurial compounds on excitable tissues. 12 2

We have shown that a Ca++-ionophore activity is present in the (Ca++ +Mg++)-ATPase of rabbit skeletal muscle sarcoplasmic reticulum (A. E. Shamoo & D. H. MacLennan, 1974. Proc. Nat. Acad. Sci. USA 71:3522). Methylmercuric chloride inhibited the (Ca++ +Mg++)-ATPase and Ca++ transport, but had no effect on the activity of the Ca++ ionophore. Mercuric chloride inhibited ATPase, transport and ionophore activity. The ATPase and transport functions were more sensitive to methylmercuric chloride than to mercuric chloride. The two functions were inhibited concomitantly by methylmercuric chloride but slightly lower concentrations of mercuric chloride were required to inhibit Ca++ transport than were required to inhibit ATPase. Methylmercuric chloride and mercuric chloride probably inhibited ATPase and Ca++ transport by blocking essential -SH groups. However, it appears that there are no essential -SH groups in the Ca++ ionophore and that mercuric chloride inhibited the Ca++ ionophore activity by competition with Ca++ for the ionophoric site. Blockage of Ca++ transport by mercuric chloride probably occurs both at sites of essential -SH groups and at sites of ionophoric activity. These data suggest the separate identity of the sites of ATP hydrolysis and of Ca++ ionophoric activity.
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PMID:Separate effects of mercurial compounds on the ionophoric and hydrolytic functions of the (Ca++ +Mg++)-ATPase of sarcoplasmic reticulum. 12 68

Some of the biochemical changes in rat kidney following the administration of mercuric chloride have been determined. Mercuric chloride had an immediate effect on the renal brush border resulting in rapid loss of the microvilli. Plasma membranes were isolated and characterised at various stages in the necrotic process, mircovilli were absent from these preparations and the activities of marker enzymes for the brush border were significantly decreased. In contrast the basal plasma membranes were unaffected by the nephrotoxin during the early stages and no change occurred in the activity of (Na+ + K+)-ATPase, a marker enzyme for the basal membranes. The change in the pattern of urinary enzyme excertion closely paralleled the ultrastructural changes in the tubular cells. The sequence of subcellular change following the administration of mercuric chloride is discussed in relation to the known mechanism of action of this agent.
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PMID:Changes in rat renal cortex, isolated plasma membranes and urinary enzymes following the injection of mercuric chloride. 14 83

Tryptic digestion of (Ca2+ + Mg2+)-ATPase from sarcoplasmic reticulum of rabbit skeletal muscle has previously been shown to cleave the enzyme initially into a 55,000-dalton fragment and a 45,000-dalton fragment. In the present study the two fragments are solubilized in sodium dodecyl sulfate (SDS) and separated by preparative polyacrylamide gel electrophoresis. The 45,000-dalton fragment is found to be a relatively nonselective, divalent cation-dependent ionophore when incorporated into an oxidized cholesterol membrane (BLM). Ionophoric activity of this fragment is inhibited by low concentrations of LaCl3, HgCl2, and various reducing agents. There appears to be one or two relatively inaccessible disulfide bonds in the 45,000-dalton fragment that are essential for transport. Addition of reducing agents inhibits the ionophoric activity of the succinylated undigested enzyme and the 45,000-dalton fragment, but has no effect on the 55,000-dalton fragment. These experiments imply that the 45,000-dalton fragment and the 55,000-dalton fragment are in a series arrangement in the membrane.
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PMID:Purification and characterization of the 45,000-Dalton fragment from tryptic digestion of (Ca2+ + Mg2+)-adenosine triphosphatase of sarcoplasmic reticulum. 15 95

A marked increase in water permeability can be induced in Xenopus oocytes by injection of mRNA from tissues that express water channels, suggesting that the water channel is a protein. In view of this and previous reports which showed that proteinases may interfere with mercurial inhibition of water transport in red blood cells (RBC), we examined the influence of trypsin, chymotrypsin, papain, pronase, subtilisin and thermolysin on water permeability as well as on ATPase activity, H(+)-pump, passive H+ conductance, and Na+/H+ exchange in apical brush-border vesicles (BBMV) and endosomal (EV) vesicles from rat renal cortex. H+ transport was measured by Acridine orange fluorescence quenching and water transport by stopped-flow light scattering. As measured by potential-driven H+ accumulation in BBMV and EV, proteinase treatment had little effect on vesicle integrity. In BBMV, ecto-ATPase activity was inhibited by 15-30%, Na+/H+ exchange by 20-55%, and H+ conductance was unchanged. Osmotic water permeability (Pf) was 570 microns/s and was inhibited 85-90% by 0.6 mM HgCl2; proteinase treatment did not affect Pf or the HgCl2 inhibition. In EV, NEM-sensitive H+ accumulation and ATPase activity were inhibited by greater than 95%. Pf (140 microns/s) and HgCl2 inhibition (75-85%) were not influenced by proteinase treatment. SDS-PAGE showed selective digestion of multiple polypeptides by proteinases. These results confirm the presence of water channels in BBMV and EV and demonstrate selective inhibition of ATPase function and Na+/H+ exchange by proteinase digestion. The lack of effect of proteinases on water transport by mercurials. We conclude that the water channel may be a small integral membrane protein which, unlike the H(+)-ATPase and Na+/H+ exchanger, has no functionally important membrane domains that are sensitive to proteolysis.
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PMID:Proteinases inhibit H(+)-ATPase and Na+/H+ exchange but not water transport in apical and endosomal membranes from rat proximal tubule. 130 58

An inhibitory receptor for cardioactive steroids such as digoxin and ouabain is located at the extracellular surface of the Na-K-adenosinetriphosphatase (ATPase) molecule. Besides cardioactive steroids, mercury is a potent inhibitor of the Na-K-ATPase activity. The half-maximal inhibitory concentration (IC50), determined within 30 min at 37 degrees C at 1 microgram protein/ml, was 200 nM, despite the presence of 1 mM EDTA; the IC50 decreased with increasing protein/inhibitor ratio, and it reached 2.7 microM at 0.1 mg protein/ml and 20 microM at 1 mg protein/ml. The IC50 for Na-K-ATPase inhibition by the diuretic compound mersalyl was 4 and 5 microM for the nondiuretic p-chloromercuribenzenesulfonic acid at 0.1 mg protein/ml. The IC50 for HgCl2 inhibition was modulated by the presence of EDTA as well as by the pump ligands Mg, Na, K, and ATP. The E2 conformation of the Na-K-ATPase molecule was more sensitive to HgCl2 than the E1 conformation. The mercury antidote 2,3-dimercapto-1-propanesulfonic acid was able to reactivate approximately 70% of the blocked enzyme. In conclusion, a metal-binding domain of the Na-K-ATPase molecule with particular high affinity for Hg(II) was described functionally in the present work. Therefore Na-K-ATPase belongs to the metal-binding proteins. Metals may modulate the cellular expression and activity of the system by interacting with its metal-binding interface.
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PMID:Mercury blocks Na-K-ATPase by a ligand-dependent and reversible mechanism. 131 20

The presence of circulating inhibitors able to decrease the renal Na-K-adenosinetriphosphatase (ATPase) activity (natriuretic hormones) was postulated some 30 years ago. In the present work, the natriuretic inhibitor HgCl2 was selected as a model compound for the structural characterization of a possible natriuretic pathway for Na-K-ATPase modification. The structural effects of Na-K-ATPase inhibition by HgCl2 were assessed by trypsinolysis of the blocked enzyme in comparison with untreated preparations. The results show that inactivation of Na-K-ATPase by HgCl2 leads to the release of the alpha-subunit from the membrane preferentially in the E2 conformation but also in the E1 conformation. Apparently, HgCl2 weakens the membrane anchoring of the alpha-subunit, presumably by loosening the alpha-beta-subunit interaction. By this mechanism, the sensitivity of the Na-K-ATPase to extracellular drugs, hormones, and antibodies, as well as to intracellular proteases and other regulatory factors, could be altered.
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PMID:Mercury weakens membrane anchoring of Na-K-ATPase. 131 21

The investigation of active Na-K transport inhibition by mercury is difficult to perform in a cell because of the presence of numerous other membrane and intracellular proteins modifiable by mercury. Thus purified Na-K-adenosinetriphosphatase (ATPase) molecules performing active transport in an artificial membrane are required to demonstrate unequivocally the inhibition of active transport by mercury. We made use of a single population of Na-K-ATPase liposomes filled with ATP and Na to show mercury inhibition of active 86Rb transport mediated by both the inside-out and right-side-out pumps in the same liposome. The effect of HgCl2 on the Na-K-ATPase in cell-like and reversed orientation was measured in comparison with convallatoxin. A dilution series showed that 10 microM externally added HgCl2 inhibited the active 86Rb transport at the cytoplasmic side first; at 50 microM both pump populations were blocked, indicating either membrane permeation by HgCl2 and inhibition at the internal intracellular domains or onset of extracellular action at higher HgCl2 concentration. The results show that the metal-binding interface of Na-K-ATPase molecule is profoundly implicated in active ion transport and that the intracellular part of the Na-K-ATPase molecule presents the primary target for mercury action.
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PMID:Mercury inhibits Na-K-ATPase primarily at the cytoplasmic side. 131 22

The effects of increasing concentrations of mercury (Hg2+) chloride (1, 2.5, 5 and 10 microM) were studied on isometrically contracting papillary muscles from female rats (Wistar, EPM strain) weighing 150 to 180 g. Hg2+ promoted an increase of 12.7 +/- 2.2% in the developed force at 1 microM. At 2.5 microM, force values were similar to control, decreasing progressively as Hg2+ concentration increased to 5 (-13 +/- 6.4%) and 10 microM (-37 +/- 12.3%). Potentiated post-rest contractions (PRC) were also determined after 15-, 30- and 60-s pauses. There was a progressive reduction of the potentiated PRCs relative to their respective steady-state control contractions with increasing concentrations of HgCl2. Since in several tissues including myocardium Hg2+ inhibits the activity of Ca2+ and Na(+)-K(+)-ATPases the results described here suggest that Hg2+, at lower concentrations, could increase force by inhibiting Na(+)-K(+)-ATPase, while at higher concentrations Hg2+ would decrease relative PRC potentiation by inhibiting sarcoplasmic reticulum Ca(2+)-ATPase.
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PMID:Effects of mercury on the contractility of isolated rat cardiac muscle. 134 26


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