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)

Polyclonal antiserum against subunit A (67 kDa) of the vacuolar ATPase from Neurospora crassa reacted with subunit I (87 kDa) from a membrane ATPase of the extremely halophilic archaebacterium Halobacterium saccharovorum. The halobacterial ATPase was inhibited by nitrate and N-ethylmaleimide; the extent of the latter inhibition was diminished in the presence of adenosine di- or triphosphates. 4-Chloro-7-nitrobenzofurazan inhibited the halobacterial ATPase also in a nucleotide-protectable manner; the bulk of inhibitor was associated with subunit II (60 kDa). The data suggested that this halobacterial ATPase may have conserved structural features from both the vacuolar and the F-type ATPases.
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PMID:Relationship of the membrane ATPase from Halobacterium saccharovorum to vacuolar ATPases. 182 11

The fluorescence of residue Trp beta 331 in beta Y331W mutant Escherichia coli F1-ATPase was used as reporter probe to investigate the effects of magnesium ions, inhibitors, and mutation on substrate (ATP) binding stoichiometry and cooperativity. It was found that Mg2+ is required for catalytic site binding cooperativity. In the absence of magnesium, ATP bound to three independent catalytic sites, each with Kd = 76 microM. In contrast, MgATP bound to three catalytic sites with Kd1 < 50 nM, Kd2 = 0.5 microM, and Kd3 = 25 microM. There was no significant ATPase activity in the absence of Mg2+. Catalysis is therefore correlated with substrate binding cooperativity and the formation of the high-affinity catalytic site 1. Catalytic site 3 had properties similar to those of the isolated beta-subunit nucleotide-binding site. The inhibitors dicyclohexylcarbodiimide and N-ethylmaleimide (in alpha S373C/beta Y331W mutant F1) gave potent inhibition of multisite ATPase activity without significantly affecting MgATP binding stoichiometry or cooperativity. Therefore each seems to selectively attenuate positive catalytic cooperativity. The same conclusions held for the alpha S373F mutation (in alpha S373F/beta Y331W mutant F1). 7-Chloro-4-nitrobenzo-2-oxa-1,3-diazole, however, reduced the catalytic site MgATP binding stoichiometry from three to two, and appears to inhibit catalysis by sterically blocking catalytic site 3.
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PMID:Cooperativity and stoichiometry of substrate binding to the catalytic sites of Escherichia coli F1-ATPase. Effects of magnesium, inhibitors, and mutation. 805 Nov 44

A multidrug-resistant Chinese hamster ovary cell line (CR1R12) was obtained which constitutively expresses P-glycoprotein, up to 32% by weight of plasma membrane protein. CR1R12 plasma membranes had high, drug-activated ATPase activity referable to P-glycoprotein. The specific ATPase activity in the presence of verapamil was calculated to be approximately 9 mumol/min/mg (identical to 21 s-1) at 37 degrees C, pH 7.4. KM ATP was 1.4 mM, and ADP and 5'-adenylyl imidodiphosphate were competitive inhibitors with Ki values 0.35 and 0.44 mM, respectively. 2'-dATP was a good substrate, GTP and ITP were real but poor substrates, and ADP and AMP were not hydrolyzed. Optimal pH for ATP hydrolysis was 7.3. MgATP was the preferred substrate, and CaATP was hydrolyzed very weakly. 7-Chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) covalently labeled the P-glycoprotein, and incorporation of 1.1 mol of NBD-Cl/mol of P-glycoprotein gave 100% inactivation. ATP protected against NBD-Cl inactivation. N-Ethylmaleimide was a potent inhibitor in the absence of ATP, and in its presence significant protection from inhibition could be achieved. Vanadate and fluoroaluminate were also strong inhibitors. The plasma membranes from CR1R12 cells should provide material for purification and reconstitution of P-glycoprotein and for screening of potential "multidrug-reversal" reagents by enzymic assay.
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PMID:Characterization of the adenosine triphosphatase activity of Chinese hamster P-glycoprotein. 809 47

7-Chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) labeled Na+/K+-ATPase covalently with two different inactivation constants (Ki = 2.5 microM; Ki' = 10 microM). It apparently modified the two different ATP-binding sites of the enzyme since it decreased the activity of the E2ATP site, i.e. the K+-activated para-nitrophenylphosphatase activity, in an enzyme whose high-affinity E1ATP site had been blocked by fluorescein 5'isothiocyanate (FITC). It also reduced the activity of the E1ATP site, i.e. the Na+-activated protein phosphorylation, in an enzyme whose low-affinity E2ATP site had been blocked by Co(NH3)4PO4. Fluorescence quenching experiments with KI, CsCl and MnCl2 of the NBD-Cl-labeled Na+/K+-ATPase revealed two differently accessible types of fluorophores depending on the ATP site: The E2ATP site apparently differs from the E1ATP site in that it is more open because the fluorophore labeling in the E2ATP site was sterically better accessible for quenchers.
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PMID:Quenching of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole-modified Na+/K+-ATPase reveals a higher accessibility of the low-affinity ATP-binding site. 942 39

7-Chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) is a specific covalent inhibitor of P-glycoprotein ATPase activity (M. K. Al-Shawi, and A. E. Senior, 1993, J. Biol. Chem. 268, 4197-4206). Complete inhibition occurs at a reaction stoichiometry of 1 mol NBD/mol P-glycoprotein, and the reagent has proved valuable in understanding catalytic mechanisms, particularly in relation to catalytic site cooperativity (A. E. Senior, and S. Bhagat, 1998, Biochemistry 37, 831-836). The actual location of reaction in the amino acid sequence has not yet been determined. Using a combined mutagenesis and biochemical approach we establish here that the initial reaction of NBD-Cl is with Cys within the Walker A consensus sequence of the N- or C-terminal nucleotide site (Cys-431 or Cys-1074 of human P-glycoprotein). Reaction with either Cys yields full inhibition. It was further found that inhibition consists of dithiothreitol (DTT)-reversible and DTT-irreversible components. The former predominates at low pH and the latter at higher pH. This demonstrates that, at higher pH, intramolecular transfer of NBD from Cys to Lys occurs, probably to the proximate Walker A Lys (Lys-433 or Lys-1076 of human P-glycoprotein). After transfer of NBD to Lys, P-glycoprotein ATPase remains fully inhibited.
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PMID:Residues in P-glycoprotein catalytic sites that react with the inhibitor 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole. 972 Nov 90