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)

1. Proteolipid was extracted from the electric organ of Narke japonica by using chloroform/methanol (2:1, v/v). This extract was separated into acetylcholine-binding and non-binding substances by column chromatography. However, acetylcholine-binding substances did not show the characteristic properties of protein. 2. The membrane fragments of the electric organ were separated into three main parts by sucrose density gradient centrifugation. From the heaviest, the fractions were acetylcholine receptor rich, ATPase rich, and acetylcholinesterase rich. 3. The membrane fraction having acetylcholine receptor showed the excitability, the increase of Na+ permeability by the application of cholinergic agonists. However, the acetylcholine binding substance extracted by the organic solvent was richer in the lighter fraction. This substance differed from the true acetylcholine receptor.
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PMID:Acetylcholine-binding substance extracted by using organic solvent and acetylcholine receptor of electric organ of Narke japonica. 12 23

Two kinetic models are introduced which predict amplitudes and time-courses of endplate currents and miniature endplate currents at neuromuscular junctions, at both normal and acetylcholinesterase-inhibited endplates. Appropriate differential rate equations reflecting interactions of acetylcholine with acetylcholine receptor and with esterase, diffusion of acetylcholine both within and from the synaptic cleft, and cooperativity between receptor site occupancy and ion channel opening are solved. Acetylcholine release into the cleft is assumed to be instantaneous. The simpler homogeneous reaction space model accurately predicts decay phase time constants are inaccurate. The two-reaction space model predicts amplitudes and time constants within a factor of two of those observed experimentally. The simulations indicate that the amplitudes and time-courses are primarily determined by the chemical reaction rates that characterize acetylcholine interactions with receptor and esterase and that these interactions occur under nonequilibrium conditions. Approximately 50% of the total ion channels in the initial reaction space are predicted to be opened at the peak endplate current. The cooperative opening of ion channels by acetylcholine requires that acetylcholine be introduced into the cleft in discrete, concentrated elements. Virtually all the open channels are confined to the initial reaction space, although acetylcholine-bound receptor sites can be much more widely distributed.
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PMID:Quantitative simulation of endplate currents at neuromuscular junctions based on the reaction of acetylcholine with acetylcholine receptor and acetylcholinesterase. 26 18

Kinetic analysis of the flux of sodium ions in a heterogeneous population of acetylcholine receptor-rich microsacs (vesicles) formed by membrane fragments of electroplax indicated that functional microsacs, which on average comprise only 15% of the preparation, can be filled with 190 mM sodium chloride while nonfunctional microsacs are filled by 190 mM cesium chloride. The functional microsacs have then been successfully separated from nonfunctional microsacs on the basis of their density differences with a continuous sucrose-190 mM cesium chloride density gradient. In the presence of acetylcholine analogs all the internal sodium ions in these microsacs rapidly exchange with external ions. The efflux of sodium ions follows a single exponential decay. The isolation of functional microsacs opens up at least two new avenues of investigation of the molecular mechanism of receptor-mediated processes. The first deals with the efficiency of the process, and the second with the characterization of membrane components important in this process. The conclusions reached so far are: (i) The efficiency of the receptor-mediated process that allows inorganic ions to equilibrate across the membranes of the microsacs can adequately account for electrophysiological results obtained with muscle and nerve cells. (ii) In the receptor-rich heterogeneous population of microsacs the concentration of receptor sites in functional and nonfunctional microsacs is about the same and is therefore not the only factor determining functionality. Significant differences between functional and nonfunctional microsacs have been found so far in the concentrations of acetylcholinesterase and Na+-K+ ATPase.
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PMID:Functional acetylcholine receptor--electroplax membrane microsacs (vesicles): purification and characterization. 26 15

Newly fused chick myotubes undergo simultaneous and rapid changes in cell membrane properties during synchronous differentiation in culture. These changes are coordinately regulated and include increases in acetylcholine receptor, acetylcholinesterase, and resting potential, as well as the appearance of action potentials in discrete membrane areas upon stimulation. Subsequently, the acetylcholine receptor reaches maximal levels, whereas the development of electrical properties is marked by a further increase in resting potential, changes in the characteristics of the elicited action potential, and the recruitment of additional membrane areas for action potential generation. Maturation of electrical excitability, marked by the acquisition of the ability to fire repetitively and to conduct action potentials along the membrane, occurs well after resting potential has reached a maximum. During post-maturational development, myotubes exhibit spontaneous electrical and contractile activity, and levels of acetylcholine receptor accessible to externally applied 125I-labeled alpha-bungarotoxin decrease markedly. It is suggested that electrophysiological membrane maturation is autonomously regulated with no requirement for neuronal intervention and involves the coordinated biosynthesis of discrete membrane components and their subsequent organization in the myotube membrane.
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PMID:Development of electrophysiological and biochemical membrane properties during differentiation of embryonic skeletal muscle in culture. 27 Jul 55

We have studied the properties of N-7-(4-nitrobenzo-2-oxa-1,3-diazole)-omega-aminohexanoic acid beta-(N-trimethylammonium)ethyl ester, a fluorescent analog of acetylcholine at the cellular level by using pharmacological and electrophysiological techniques and at the molecular level by measuring the kinetics of interaction with solubilized acetylcholine receptor and with acetylcholine esterase (EC 3.1.1.7). The fluorescent drug is a powerful agonist of acetylcholine at the neuromuscular junction and also strongly desensitizes muscle fibers. Interaction with acetylcholine receptor is accompanied by large changes in the drug's fluorescence. From the kinetics of interaction studied by means of a stopped-flow fluorimeter with laser light source, we obtained a second-order forward rate constant in excess of 1 X 10(8) M-1 sec-1 and an initial dissociation rate constant (k1) of 0.5 sec-1 for receptor from Electrophorous electricus. Interaction of this analog with acetylcholine esterase from E. electricus is accompanied by a transient decrease in fluorescence followed by an increase leading to a stable plateau value at a level near the original one. The initial decrease in fluorescence followed second-order kinetics with k2 of the order of 10(9) M-1 sec-1. The slower consecutive reaction which could be blocked by phosphorylation of the esteratic site, was of first order with k1 = 0.05 sec-1.
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PMID:NBD-5-acylcholine: fluorescent analog of acetylcholine and agonist at the neuromuscular junction. 31 97

Chronic paralysis of Chick embryos by the cholinergic antagonist flaxedil blocks the subsynaptic accumulation of acetylcholinesterase but not the formation of acetylcholine receptor cluster. Flaxedil paralysis also causes an increase of the total muscle content of acetylcholine receptor without altering the half-life of the receptor protein. The spontaneous activity of the embryon therefore "shuts off" the synthesis of extrasynpatic acetylcholine receptor.
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PMID:[Effects of chronic paralysis of chick embryo by flaxedil on the development of the neuromuscular junction]. 41 64

A system has been developed for the detailed analysis of the transition from proliferative myoblast to differentiated muscle cell. Dimethylsulfoxide (DMSO) prevents the terminal differentiation of L8 myoblasts in vitro, and its effect is reversible. DMSO (2%) inhibits the fusion of myoblasts to form multinucleate myotubes, the normal increases in activity of creatine phosphokinase (CPK) and acetylcholinesterase, and the synthesis of alpha-actin and acetylcholine receptor protein. Upon removal of DMSO from the medium, a lag precedes the onset of differentiation. The potential to inhibit muscle differentiation reversibly is not specific to DMSO, but is shared by a number of compounds, including dimethylformamide, hexamethylbisacetamide and butyric acid, all potent inducers of gene expression in Friend erythroleukemia cells. L8 cells routinely cease DNA synthesis and initiate fusion and muscle protein synthesis once they are confluent. In the presence of DMSO, however, nearly all cells continue DNA synthesis, even several days after reaching confluence. Protein synthetic patterns of DMSO-inhibited cells are almost indistinguishable from those of untreated myoblasts and distinct from differentiated myotubes. It appears that cells exposed to DMSO are locked indefinitely in a proliferative myoblast stage of development and are unable to enter the Go phase of the cell cycle necessary for initiation of differentiation. DMSO coordinately inhibits all the differentiative parameters measured. In contrast, cytochalasin B uncouples normally linked differentiative events so that fusion is inhibited while muscle-specific protein synthesis proceeds. DMSO has similar effects on both cytochalasin B-treated and fusing control cultures, suggesting that its primary effect is exerted not at the level of fusion but earlier in the differentiative time-table. Once fusion and the synthesis of muscle-specific proteins are well under way, the addition of DMSO is ineffective and differentiation continues in its presence. The potential to manipulate muscle gene expression in vitro makes this system particularly useful for the detailed analysis of the processes involved in the transition to the differentiated state and for determining the linkage of developmental events.
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PMID:Manipulation of myogenesis in vitro: reversible inhibition by DMSO. 45 62

The interaction of acetylcholine receptor and acetylcholinesterase with lipid monolayers was followed by measuring changes in surface pressure. When injected into the subphase of a lipid monolayer, the proteins caused increases in surface pressure from 5 to 10 dynes/cm, indicating a penetration of protein into the monolayer. At pH values below the isoelectric point of the proteins the incorporation was improved. The same was observed when Ca2+ (2mM) was added. The presence of the enzyme in the mixed film could be demonstrated by using diiso [3H] propyl fluorophosphate-labelled acetylcholinesterase as well as by measuring enzyme activity. Acetylcholine receptor was shown to be present in the mixed film by using a complex made of the receptor and alpha-[3H]neurotoxin.
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PMID:Interactions of acetylcholine receptor and acetylcholinesterase with lipid monolayers. 62 25

Characterization of acetylcholine-receptor-enriched membranes from Torpedo californica electric tissue by negative-staining electron-microscopy and by lipid analysis is described. The protein/lipid ratio is 70%/30%. The lipids consist of 70% phospholipids (46% phosphatidylcholine, 31% phosphatidylethanolamine, 14% phosphatidylserine, 7% sphingomyelin, 2% phosphatidylinositol of the phospholipids determined) and 20% cholesterol. The acetylcholinesterase-enriched membranes show a similar composition. The only differences are a lower protein/lipid ratio (45%/55%) and a lower phosphatidylcholine/sphingomyelin ratio of 39%/14% as compared to 46%/7% for the receptor-enriched membranes. A method of preparing single-walled phosphatidylcholine vesicles by gel filtration on Sephadex G50 according to Brunner et al. (Biochem. Biophys. Acta, 455, 322--331, 1976) is used to recombine the lipid-depleted receptor complex with artificial lipid vesicles. Starting from a lipid mixture of 46% phosphatidylcholine, 31% phosphatidylethanolamine, 14% phosphatidylserine, 7% sphingomyelin, 2% phosphatidylinositol and 15% cholesterol we obtained vesicles associated with the acetylcholine receptor complex. These receptor vesicles are chemically excitable by 10 micrometer carbamoylcholine as measured by efflux of 22Na+ from the vesicles. The excitability is blocked by preincubation with 0.5 mM alpha-toxin from Naja naja siamensis venom and by reduction with 5 mM dithioerythritol.
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PMID:Membranes rich in acetylcholine receptor: characterization and reconstitution to excitable membranes from exogenous lipids. 63 24

Activity of the enzyme choline acetyltransferase (CAT), which mediates the synthesis of the neurotransmitter, acetylcholine, was increased up to 20- fold in spinal cord (SC) cells grown in culture with muscle cells for 2 wk. This increase was directly related to the duration of co-culture as well as to the cell density of both the SC and muscle involved and was not affected by the presence of the acetylcholine receptor blocking agent, alpha-bungarotoxin. Glutamic acid decarboxylase (GAD) activity was often markedly decreased in SC-muscle cultures while the activities of acetylcholinesterase and several other enzymes were little changed. Increased CAT activity was also observed when SC cultures were maintained in medium which had been conditioned by muscle cells or by undifferentiated cells from embryonic muscle. Muscle-conditioned medium (CM) did not affect the activities of SC cell GAD or acetylcholinesterase. Dilution or concentration of the CM directly affected its ability to increase SC CAT activity , as did the duration and timing of exposure of the SC cells to the CM. The medium could be conditioned by muscle cells in the presence or absence of serum, and remained effective after dialysis or heating to 58 degrees C. Membrane filtration data were consistent with the conclusion that the active material(s) in CM had a molecular weight in excess of 50,000 daltons. We conclude that large molecular weight material that is released by muscle cells is capable of producing a specific increase in CAT activity of SC cells.
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PMID:Choline acetyltransferase activity of spinal cord cell cultures increased by co-culture with muscle and by muscle-conditioned medium. 87


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