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:3.1.1.7 (acetylcholinesterase)
28,390 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cholinesterases are serine hydrolases that show no global similarities in sequence with either the trypsin or the subtilisin family of serine proteases. The cholinesterase superfamily includes several esterases with distinct functions and other proteins devoid of the catalytic serine and known esterase activity. To identify the residues involved in catalysis and conferring specificity on the enzyme, we have expressed wild-type Torpedo acetylcholinesterase (EC 3.1.1.7) and several site-directed mutants in a heterologous system. Mutation of serine-200 to cysteine results in diminished activity, while its mutation to valine abolishes detectable activity. Two conserved histidines can be identified at positions 425 and 440 in the cholinesterase family; glutamine replacement at position 440 eliminates activity whereas the mutation at 425 reduces activity only slightly. The assignment of the catalytic histidine to position 440 defines a rank ordering of catalytic residues in cholinesterases distinct from trypsin and subtilisin and suggests a convergence of a catalytic triad to form a third, distinct family of serine hydrolases. Mutation of glutamate-199 to glutamine yields an enzyme with a higher Km and without the substrate-inhibition behavior characteristic of acetylcholinesterase. Hence, modification of the acidic amino acid adjacent to the serine influences substrate association and the capacity of a second substrate molecule to affect catalysis.
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PMID:Mutagenesis of essential functional residues in acetylcholinesterase. 221 85

Male rats administered with a single i.p. dose of 5 mg/kg methyl parathion, showed the toxic signs of hypercholinergic (anticholinesterase) activity with maximal severity, including muscle fasciculations and convulsions within 15 to 30 min, persisting for about 2 hr. The time course of acetylcholinesterase activity in discrete brain regions (cortex, stem, striatum and hippocampus), heart and hemidiaphragm, indicated its maximal depression during 30 to 60 min after administration of methyl parathion. At this time, a marked reduction in carboxylesterase activity was also evident both in neuronal and nonneuronal tissues, suggesting a tremendous binding to nonacetylcholinesterase serine sites. Pretreatment with memantine hydrochloride (18 mg/kg, i.p.) 30 min, and atropine sulfate (16 mg/kg, i.p.) 15 min before methyl parathion administration, completely prevented the expected toxic signs and significantly (P less than 0.01) attenuated the induced inhibition of acetylcholinesterase. When given therapeutically, this combined treatment completely reversed the clinical evidence of methyl parathion toxicity within 10 to 15 min and markedly reduced the acetylcholinesterase inactivation. These results suggest that memantine may counteract the acute methyl parathion toxicity by (a) protection of acetylcholinesterase from inhibition, (b) rapid reactivation of inhibited acetylcholinesterase and (c) rapid bioelimination of methyl parathion, in addition to cholinolytic effects of atropine sulfate.
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PMID:Methyl parathion acute toxicity: prophylaxis and therapy with memantine and atropine. 224 28

About 30% of the primary structure of acetylcholinesterase (AchE) from the cobra Naja naja oxiana has been determined. The sequence around the serine residue labeled by diisopropylfluorophosphate (DFP) was found to be TVTLFGESAGAASVGM which is similar to the active sites of AChE from other tissues. The part of the primary structure determined shows 76% identity with AChE from Torpedo and 42% identity with the Drosophila enzyme. A surprisingly large identity (42% in the sequence determined) was found with lysophospholipase from rat.
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PMID:The active site and partial sequence of cobra venom acetylcholinesterase. 234 76

Nonadrenergic, noncholinergic contractile responses of guinea pig hilar bronchi to transmural electrical stimulation (TES) have been suggested to be due to release of endogenous tachykinins from capsaicin-sensitive neurons (C-fibers). Thiorphan and phosphoramidon, inhibitors of neutral endopeptidase (NEP, the major enzyme responsible for degrading tachykinins), were found to potentiate contractile responses of this isolated airway segment to TES and exogenously applied capsaicin, substance P and neurokinin A. However, the magnitude of potentiation by either inhibitor was smaller for TES and capsaicin (less than 10-fold leftward shift) than for the substrate agonists (about 100-fold leftward shift). This quantitative difference in potentiation by NEP inhibitors does not appear to be due to an influence of vasoactive intestinal peptide or calcitonin gene-related peptide, two endogenous peptides that might be released concomitantly by TES. Neither peptide caused marked effects on contractile responses to TES or tachykinins when applied to the isolated tissues. Addition of inhibitors of serine proteases, aminopeptidases, acetylcholinesterase and angiotensin-converting enzyme failed to further potentiate responses to TES in the presence of thiorphan. Therefore, the contractile response does not appear to be further modified by the activity of these peptidases. Neuropeptide gamma, but not neuropeptide K, was potentiated by thiorphan. The data suggest that peptides that are not substrates for NEP (for example, neuropeptide K) may also be released by TES from capsaicin-sensitive neurons to cause contraction. This may, at least in part, explain the quantitative difference in potentiation by NEP inhibitors of contractile responses to TES and to exogenously applied NEP-sensitive tachykinins in the guinea pig hilar bronchus.
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PMID:Pharmacologic studies on the differential influence of inhibitors of neutral endopeptidase on nonadrenergic, noncholinergic contractile responses of the guinea pig isolated hilar bronchus to transmural electrical stimulation and exogenously applied tachykinins. 239 13

Hybridomas secreting monoclonal antibodies to Nippostrongylus brasiliensis antigens were generated by hybridization of IR983F myeloma cells with spleen cells from Lou/M/Wol rats infected with living third-stage larvae. Antibodies specific either for larval or worm antigens were identified by enzyme-linked immunosorbent assays with Nippostrongylus brasiliensis fragments, homogenates and secretions as antigens. The results demonstrate that all antibodies which recognized larval antigens (38 antibodies) also reacted with worm surfaces. Ten antibodies were specific only for worm antigens. Ten antibodies reacted with worm homogenate, three antibodies recognized components of worm secretion and 17 antibodies combined with acetylcholinesterase. The epitope specificity was investigated by the capacity of various glycosides, aminoacids, N-acetylneuraminic acid and phosphorylcholine to inhibit the binding to worm fragments. The analysis revealed that alpha-methylglucoside, alpha-methylmannoside, N-acetylglucosamine, N-acetylgalactosamine, fucose and the amino acids leucine, phenylalanine, tyrosine, serine, tryptophan did not combine with the antigen-binding sites of the antibodies. Proline, arginine and histidine, however, displayed inhibitory effects. With N-acetylneuraminic acid as inhibitor three groups of antibodies could be discriminated. At a concentration of 10-20 mM, phosphorylcholine was a potent inhibitor for all antibodies.
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PMID:Characterization of antigens of the nematode Nippostrongylus brasiliensis by monoclonal antibodies. 241 42

To determine the role of endogenous neutral endopeptidase (NEP), also called enkephalinase (EC 3.4.24.11), in regulating tachykinin-induced contraction of gut smooth muscle, we studied the effects of NEP inhibitors on the contractile responses to substance P (SP) in isolated longitudinal strips of ileum or duodenum in rats and ferrets. Leucine-thiorphan and phosphoramidon shifted the concentration-response curves of SP to lower concentrations in all tissues studied, but the sensitivity to SP was greater and the effect of leucine-thiorphan was less in the ferret, a finding that correlated with the observation that the ferret ileum contained substantially less NEP activity than rat ileum. Captopril, bestatin, MGTA, leupeptin, and physostigmine did not alter contractile responses to SP, suggesting that kininase II, aminopeptidases, carboxypeptidase N, serine proteinases, and acetylcholinesterase do not modulate the SP-induced effects. These studies suggest that, in the ileum and duodenum, NEP modulates the actions of SP and, furthermore, that the sensitivity of tissues may be determined, at least in part, by the amount of enzymatically active NEP present.
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PMID:Neutral endopeptidase inhibitors potentiate substance P-induced contraction in gut smooth muscle. 246 69

Procedures for loading fura 2 acetoxymethyl ester (fura 2/AM) into smooth muscle cells isolated from guinea pig taenia coli have been investigated. It was difficult to load these cells with fura 2 in the absence of diisopropylfluorophosphate (DFP). The presence of DFP, a potent cholinesterase (ChE) inhibitor during the loading, significantly enhanced the incorporation of the fura 2 into the cells. More than 80% of the single cells treated with DFP and fura 2/AM were viable. DFP did not affect the ability of the cell to shorten in response to either Ca2+ or carbachol (CCh). The single cells contracted transiently with caffeine and the intracellular Ca2+ concentration increased simultaneously. The results indicate that the amount of fura 2/AM incorporated into the single smooth muscle cells depends on the activity of ChE or various serine proteases located outside the cells and suppression of these enzymes induces more efficient incorporation, which permits shorter incorporation periods. Since the presence of DFP may shorten the incubation time significantly, the viability of these cells is improved. The procedure might be applicable for measuring simultaneously the contraction of cells and the behavior of intracellular Ca2+ in the same cells.
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PMID:Loading of fura-2/AM with an aid of DFP on single smooth muscle cells prepared from guinea pig taenia coli. 249 88

We and others have recently described 9-O-acetyl-sialic acid esterase (9-O-Ac-SA esterase) activities that appear to be specific for removal of O-acetyl esters from the 9-position of naturally occurring sialic acids. We have now examined a variety of species for such enzymes and found them in vertebrates and higher invertebrates, but not in plants or in lower invertebrates. This evolutionary distribution correlates well with that of the sialic acids themselves. All of the 9-O-Ac-SA esterase activities tested were inhibited by diisopropyl fluorophosphate (DFP) in a dose-dependent fashion. This indicates that each of these enzymes has a serine active site similar to the well known serine esterases and serine proteases. Methyl esterification of the carboxyl group of 9-O-acetyl-N-acetylneuraminic acid significantly reduced the activity of all of the 9-O-Ac-SA esterases against the O-acetyl group. This indicates that each of these enzymes may recognize the negatively charged carboxyl group of the sialic acid. Enzymes that recognize anionic substrates frequently have an essential arginine residue (Riordan, J. F., McElvany, K. D., and Borders, C. L., Jr. (1977) Science 195, 884-886). We therefore studied the effects of the arginine-specific modifying reagents 2,3-butanedione and phenylglyoxal on 9-O-Ac-SA esterase activities from influenza C virus, human erythrocytes, rat liver, starfish gonads, and sea bass brain. All of these enzymes were inhibited in a dose-dependent fashion by both reagents, under conditions previously known to avoid nonspecific modification. In contrast, the typical serine proteases trypsin and kallikrein and the serine esterase acetylcholinesterase were not significantly affected, even by the highest concentrations of these reagents used. These data indicate that five 9-O-Ac-SA esterase activities from evolutionarily distinct origins all have serine active sites and essential arginine residues. We postulate that the arginine residue is involved in substrate recognition via the negatively charged carboxyl group of the sialic acids. Thus, these 9-O-Ac-SA esterase activities may be members of a previously undescribed class of serine esterase.
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PMID:O-acetylation and de-O-acetylation of sialic acids. Sialic acid esterases of diverse evolutionary origins have serine active sites and essential arginine residues. 250 78

The peptidasic site of highly purified human plasma cholinesterase was investigated using active-site-directed inhibitors. Peptidase activity was assayed taking substance P as substrate. Inhibition by organophosphates indicated that the peptidasic site contained an active serine. The presence of essential histidine residues associated with serine was revealed by histidine modifications. Carboxyl group reagents showed that the active centre contained carboxyl groups in a non-polar environment. The removal of sialic acids did not alter peptidase activity. The peptidasic site of cholinesterase shared many properties with serine proteases sites and esteratic sites of cholinesterases. In addition, with the peptidasic site, as well as the esteratic site, there was always the possibility of 'aging' when inhibited by DFP or soman.
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PMID:Study of the peptidasic site of cholinesterase: preliminary results. 257 54

Human serum cleaves two dipeptides from the N-terminus of the neurohormone substance P. It has been suggested that this degrading activity is inherent to serum cholinesterase. We oppose this, because it turned out that highly purified serum cholinesterase contains traces of dipeptidyl peptidase IV, an enzyme known to attack the N-terminus of substance P. The peptidase is incompletely separated from cholinesterase during the procainamide-gel affinity chromatography as the last step of the usual purification procedure. Physostigmine completely inhibits the hydrolysis of butyrylthiocholine by such purified cholinesterase preparations, but not their substance P-degrading activity. Vice versa, epsilon-carbobenzoxy-lysylproline, an inhibitor of dipeptidyl peptidase IV, inhibits the peptidase activity of these preparations more than their esterase activity. After rechromatography on procainamide gel the peptidase is completely separated and the remaining cholinesterase has lost its substance P-degrading activity. We conclude that the N-terminal region of substance P is not degraded by cholinesterase but by the contaminating dipeptidyl peptidase IV, a different serine enzyme.
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PMID:Substance P in human plasma is degraded by dipeptidyl peptidase IV, not by cholinesterase. 258 Sep 48


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