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)

1. The distribution of acetylcholine (ACh) sensitivity was mapped in skeletal twitch muscles of the snake, frog and mudpuppy with iontophoretic methods that provide a resolution in the mum range. 2. The preparations were thin sheets of muscle fibres that were viewed with Nomarski optics, giving sharp definition of cellular detail. The muscles in the snake were especially suitable. Their motor nerves terminate in a compact cluster of synaptic boutons that rest in distinct craters on the muscle surface. After treatment with collagenase the motor nerve and its terminal boutons can be removed, exposing the subsynaptic membrane in the craters. 3. The slopes of dose-response curves obtained by iontophoretic application of ACh were expressed in mV/nC and used as an index of ACh sensitivity. The areas of highest sensitivity, tested either with the terminals in place or removed, were those immediately under the presynaptic terminals. The greatest subsynaptic sensitivities were about 5000 mV/nC, and the time course of the potentials caused by ACh released iontophoretically closely matched that of synaptic potentials set up by ACh released by the nerve. 4. The sensitivity of the extrasynaptic surface less than 2 mum away was at least 50 times lower than that of the subsynaptic membrane. The low extrasynaptic sensitivity declined still further at greater distances. 5. Acetylcholinesterase was shown physiologically to be confined to subsynaptic areas. No activity of the enzyme was detected in extrasynaptic areas beyond about 2 mum from the edge of the synapse. 6. The confinement of high densities of receptors and of acetylcholinesterase to the subsynaptic membrane in muscles is also a feature in parasympathetic neurones. It is suggested that similar specialization may be a widespread property of neurones with chemical synapses.
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PMID:The distribution of acetylcholine sensitivity at the post-synaptic membrane of vertebrate skeletal twitch muscles: iontophoretic mapping in the micron range. 16 60

1. End-plate currents have been studied in gylcerol-treated frog sartorius nerve-muscle preparations with the voltage-clamp technique. 2. Adding the anticholinesterase prostigmine (3 muM) to the solution bathing the muscle caused a 2-7 (mean 3-3) times increase in the time constant of decay of end-plate currents. The anticholinesterase edrophonium (15 muM) also prolonged the time course of end-plate currents. 3. Pre-treatment of the preparation with collagenase, which leads to the removal of acetylcholinesterase in the synaptic cleft, prolongs the time course of end-plate currents. 4. Curare (1-2 muM), cobratoxin (0-13 muM), or alpha-bungarotoxin (0-13-0-26 muM) decreased the time constant of decay of end-plate currents in the presence of prostigmine. 5. These observations are consistant with the suggestion that repeated binding of acetylcholine (ACh) molecules to receptors as the ACh escapes from the synaptic cleft can contribute to the prolongation of end-plate currents which occurrs when acetylcholinesterase activity is eliminated. 6. Increasing the amount of transmitter released from the presynaptic nerve terminal leads to a prolongation of end-plate currents in the presence of prostigmine. 7. In the presence of prostigmine, the second of two end-plate currents (interval 2-10 msec) decays more slowly than the first. 8. ACh (1-40 muM) or carbachol (40 muM) applied in the solution bathing the muscle prolongs end-plate currents in the presence of prostigmine. 9. It is suggested on the basis of the observations described in paragraphs 6 to 8 that the time constant of decay of end-plate currents in the presence of prostigmine increases with increasing concentrations of ACh in the synaptic cleft. In the absence of prostigmine, increasing the concentration of ACh in the synaptic cleft did not change the time constant for decay of end-plate currents. 10. We interpret these results to suggest that ACh can have a cooperative action on receptors such that the association of ACh with one receptor (defined as binding a single ACh molecule) favours the binding or retention of ACh at other receptors. This implies that receptors can interact.
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PMID:Factors affecting the time course of decay of end-plate currents: a possible cooperative action of acetylcholine on receptors at the frog neuromuscular junction. 16 52

The 16S and 8S forms of acetylcholinesterase (AchE), which are composed of an elongated tail structure in addition to the more globular catalytic subunits, were extracted and purified from membranes from Torpedo californica electric organs. Their subunit compositions and quaternary structures were compared with 11S lytic enzyme which is derived from collagenase or trypsin treatment of the membranes and devoid of the tail unit. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the absence of reducing agent, appreciable populations of monomeric through tetrameric species are observed for the 11S form. Under the same conditions, the 16S form yields only monomer and dimer in addition to a higher molecular weight species. If complete reduction is effected, only the 80,000 molecular weight monomer is dominant for both the 11S and 16S forms. Cross-linking of the 11S form by dimethyl suberimidate followed by reduction yields monomer through tetramer in descending frequency, while the 16S form again shows a high molecular weight species. A comparison of the composition of the 11S and 16S forms reveals that the latter has an increased glycine content, and 1.1 and 0.3 mol % hydroxyproline and hydroxylysine, respectively. Collagenases that have been purified to homogencity and are devoid of amidase and caseinolytic activity, but active against native collagen, will convert 16S acetylcholinesterase to the 11S form. Thus, composition and substrate behavior of the 16S enzyme are indicative of the tail unit containing a collagen-like sequence. A membrane fraction enriched in acetylcholinesterase and components of basement membrane can be separated from the major portion of the membrane protein. The 16S but not the 11S form reassociates selectively with this membrane fraction. These findings reveal distinct similarities between the tail unit of acetylcholinesterase and basement membrane components and suggest a primary association of AchE with the basement membrane.
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PMID:Molecular forms of acetylcholinesterase from Torpedo californica: their relationship to synaptic membranes. 17 42

Tailed forms of Electrophorus acetylcholinesterase, mainly A (9 S) and C (14.2 S) forms, have been subjected to collagenase treatment. Several steps have been identified, yielding molecules which have lost different portions of the tail, and eventually resulting in separation of the isolated tetramers. These modifications result in the disappearance of the low-ionic strength aggregating properties. The molecules which have retained relatively large fragments of the tail do not aggregate in the same conditions as the intact forms, but still form small aggregates in the presence of high levels of polyanions. A model of the tailed molecules, illustrating the existence of discrete collagenase-sensitive regions in the tail, is discussed.
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PMID:Collagenase sensitivity and aggregation properties of Electrophorus acetylcholinesterase. 21 72

The assymmetric 18S and 14S forms of acetylcholinesterase (EC 3.1.1.7) from Electrophorus electricus purified by affinity chromatography on N-methylacridinium Sepharose 2B were subjected to trypsin or collagenase proteolysis and changes in the enzyme composition and structure were monitored by sucrose gradient sedimentation, gel chromatography, and sodium dodecyl sulphate - polyacrylamide gel electrophoresis. A distinction between autolytic and tryptic degradation products is described and the generation of two new forms of acetylcholinesterase from the 18S and 14S enzyme by collagenase proteolysis is reported. The species derived from the 18S form of acetylcholinesterase has a sedimentation coefficient of 21.1S and a Stokes radius of 12.9 nm while the 14S form gives rise to a 17.3S species with a Stokes radius of 11.1 nm. The proteolytically sensitive component ('tail') of the asymmetric forms of acetylcholinesterase is identified with a subunit of 45 000 daltons on sodium dodecyl sulphate - polyacrylamide electrophoresis gels.
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PMID:Acetylcholinesterase: characterization of native and proteolytically derived forms and identification of structural protein components. 21 47

We have identified six molecular forms of acetylcholinesterase (AcChoE: acetylcholine hydrolase, EC 3.1.1.7) in extracts from bovine superior cervical ganglia. We show that three of them resemble the collagen-tailed forms of Electrophorus AcChoE in their hydrodynamic parameters, low-salt aggregation properties, and collagenase sensitivity. The six molecular forms of bovine AcChoE appear structurally homologous to the six forms of electric fish AcChoE that have previously been characterized. They include globular molecules (monomers, dimers, and tetramers) and asymmetric aggregating molecules that possess a collagen-like tail associated with one, two, and three tetramers. We propose to call the globular forms G1, G2, and G4 and the asymmetric forms A4, A8, and A12, the subscripts indicating the number of catalytic subunits. In spite of quantitative differences in their molecular parameters, the AcChoE forms from rat and chicken are clearly homologous to those of bovine AcChoE. Thus the nomenclature we introduce is very probably valid for the main AcChoE molecular forms, at least in vertebrates, and should help to clarify structural relationships and homologies among them. This model, however, does not claim to represent entirely the complex polymorphism of AcChoE, because more or less hydrophobic variants of the G forms have been observed, and because other molecular associations cannot be excluded. We discuss the significance of the globular and collagen-tailed structure for the molecular localization of AcChoE.
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PMID:Asymmetric and globular forms of acetylcholinesterase in mammals and birds. 28 44

1. Quantitative ionophoresis at the neuromuscular junction is possible when (a) the drug is released from appropriate distances (15--20 micrometer for most drugs), (b) the topology of receptors is known and (c) high resistance drug pipettes (100--200 M omega) are sued. 2. With this method, drug concentration-endplate conductance relations were determined in voltage-clamped end-plates of the frog for the agonists ACh, carbamylcholine (CCh) and suberyldicholine (SubCh). 3. Based on the co-operative and independent model, theoretical dose-response curves were computed using as parameters the Hill coefficient nH, maximum conductance gmax., and apparent dissociation constant K. It was found that the co-operative model fitted the data much better than the independent model. 4. Based on the co-operative model, the mean maximum conductance for ACh was gmax. = 169 nS/micrometer, equivalent to 9000 ionic channels/micrometer length of a nerve terminal which can be opened at high drug concentrations. 5. The maximum conductance for CCh at--80 mV membrane potential was, on the average, 78% of that for ACh measured at the same end-plates. This value is termed the relative efficacy of CCh. 6. The mean values for the apparent dissociation constant K were 27.8 micrometer for ACh, 336 micrometer for CCh and 18 micrometer for SubCh. 7. The inhibition of the acetylcholinesterase activity by edrophonium (3--10 micrometer) affected only the local ACh concentration at the receptor sites, but not gmax. and nH. 8. Dose-response curves measured before and after removal of single nerve terminals in collagenase-treated muscle fibres showed no change in the nH, gmax. and K. A slight increase in gmax. to a value of 218 nS/micrometer observed comparing collagenase-treated and untreated end-plate. 9. Desensitization of receptors may occur in the range of several tens of milli-seconds.
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PMID:Determination of dose-response curves by quantitative ionophoresis at the frog neuromuscular junction. 30 3

The four molecular forms of chick embryo leg muscle acetylcholinesterase have been isolated by velocity sedimentation; their apparent sedimentation coefficients are 19.5 S, 11.5 S, 7.1 S, and 5.4 S. All four forms are glycoproteins, exhibit the same Km for acetylcholine, and are inhibited to the same extent by specific inhibitors of acetyl- and buryrylcholinesterase. Treatment of the 19.5 S form of acetylcholinesterase with trypsin generates an array of molecular forms, several of which have sedimentation coefficients identical with the naturally occurring forms. Collagenase treatment of the 19.5 S acetylcholinesterase results in a somewhat different pattern of acetylcholinesterase forms including a novel 20.6 S form. Only the 19.5 S acetylcholinesterase is sensitive to collagenase treatment. Our results indicate that the several acetylcholinesterase forms share a common catalytic subunit, and suggest that the molecular forms of acetylcholinesterase in the chick represent different ensembles of a common monomer. In culture, the muscle cells contain only the 11.5 and 7.1 S acetylcholinesterase forms; however, they also secrete substantial amounts of enzyme into the medium. These secreted acetylcholinesterases have sedimentation coefficients of 9 S and 15 S. The relative abundance of the different acetylcholinesterase molecular forms changes during muscle development, both in vivo and in vitro, suggesting that the assembly and distribution of this family of membrane glycoproteins is developmentally regulated.
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PMID:Molecular forms of chicken embryo acetylcholinesterase in vitro and in vivo. Isolation and characterization. 57 40

Release of peroxidase from secretory cells of rat lacrimal gland upon cholinergic stimulation was studied in vitro with single lobules and isolated cells (lacrimocytes). Isolated lobules, kept in Eagle's medium, remain structurally intact and reaction product of peroxidase is confined to cisternae of rough endoplasmic reticulum, elements of the Golgi apparatus, and all secretory granules. Morphologically, exocytosis occurs by membrane fusion and discharge of granule content. The highest rate of peroxidase released from lobules is observed at 10(-4) M carbamylcholine. The specific activity of peroxidase released into the medium is fourfold higher as compared to the lobules. Release of peroxidase is suppressed by atropine when added before or after the addition of carbamylcholine. At 4 degrees C, no peroxidase release occurs upon cholinergic stimulation. The exocytotic release of peroxidase is dependent on energy supply, as indicated by substantial inhibition (at 37 degrees C) under anoxic conditions or in the presence of dinitrophenol, KCN, or carboxyatractyloside. Furthermore, the process is sensitive to colchicine and vinblastine. Isolated lacrimocytes, consiting of 95% secretory acinar cells, are prepared by digestion with collagenase, hyaluronidase, and trypsin. They retain the characteristic polarity of secretory cells in situ, and localization of peroxidase is the same as in lobules. Since isolated lacrimocytes respond to cholinergic stimulation in the same way as lobules, the receptors are not damaged by the isolation procedure and appear to be associated directly with the exocrine cell. Oxygen uptake by isolated lacrimocytes is about 14 nmol O2 X min-1 X 10(-6) cells; it is about doubled by uncoupling with dinitrophenol. Oxygen uptake rises by 20-30% above the resting rate upon cholinergic stimulation. This additional uptake is suppressed by atropine or by added cholinesterase, indicating that continuous receptor occupancy may be required for the energy demand by exocytosis. On the basis of the specific activity of peroxidase in the medium, the energy demand resulting from cholinergic stimulation is estimated to be 0.08 mumol ATP (or energy-rich phosphate bonds) per microgram of protein released from the lacrimocytes.
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PMID:Exocytosis in secretory cells of rat lacrimal gland. Peroxidase release from lobules and isolated cells upon cholinergic stimulation. 95 71

In frog cutaneous-pectoris muscles the frequency of slowly rising atypical miniature endplate potentials (MEPPs) was significantly enhanced after collagenase (0.1%) treatment. Treatment with trypsin, hyaluronidase, hyper- and hypoosmotic solutions caused no changes in slowly rising MEPP (frequency in muscle fibers with intact acetylcholinesterase (AChE). Inhibition of AChE caused appearance of giant MEPPs. Acceleration of acetylcholine diffusion from synaptic cleft after treatment with hyaluronidase decreased giant MEPP frequency demonstrating their dependence upon nonhydrolyzed acetylcholine in synaptic cleft. The relation between slowly rising MEPPs and activity of synaptic Schwann cells in discussed.
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PMID:[Atypical endplate miniature potentials in the frog neuromuscular junction after modification of the intercellular matrix and osmotic exposures]. 129 72


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