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)

This study examines the importance of electrostatic interactions on ligand association at the active center of acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7). The active-center serine was covalently modified with the dimensionally equivalent isosteric beta-(trimethylammonium)ethyl and 3,3-dimethylbutyl methylphosphonofluoridates. Reactivation of the 3,3-dimethylbutyl methylphosphono-conjugate by the bisquaternary mono-oxime HI-6, after accounting for the capacity for spontaneous reactivation, proceeded at a rate that was 20-fold greater than that for the cationic conjugate. Decidium, a fluorescent bisquaternary ligand that binds with its trimethylammonium moiety within the active center, exhibited affinity for the 3,3-dimethylbutyl conjugate that was within 2-fold that for the native enzyme, but 100-fold greater than for the cationic conjugate. Whereas association of n-alkyl mono- and bisquaternary ligands with the uncharged conjugate was virtually unaltered with respect to the native enzyme, the affinities of edrophonium, phenyltrimethylammonium and N-methylacridinium were reduced 100-fold for the uncharged conjugate relative to native enzyme. These results indicate that the orientations of the 3,3-dimethylbutyl and beta-(trimethylammonium)ethyl moieties with respect to the surface of the enzyme are not equivalent, that modification of the active center does not preclude cation association of active-center-selective ligands, and that aromatic cations associate at an anionic locus which is unique from that at which decidium and the n-alkyl mono- and bisquaternary cations associate. As such, the results point to the presence of a heterogeneity of cation binding sites within a circumscribed distance from the modified serine, and do not sustain the view proposed by Hasan et al. (J. Biol. Chem. 255 (1980) 3898-3904; 256, (1981) 7781-7785) that electrostatic interactions at the active center are subordinate to steric constraints imposed by a dimensionally restricted trimethyl site.
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PMID:Kinetic, equilibrium and spectroscopic studies on cation association at the active center of acetylcholinesterase: topographic distinction between trimethyl and trimethylammonium sites. 308 81

Human serum cholinesterase was digested with pepsin under conditions which left disulfide bonds intact. Peptides were isolated by high pressure liquid chromatography, and those containing disulfide bonds were identified by a color assay. Peptides were characterized by amino acid sequencing and composition analysis. Human serum cholinesterase contains 8 half-cystines in each subunit of 574 amino acids. Six of these form three internal disulfide bridges: between Cys65-Cys92, Cys252-Cys263, and Cys400-Cys519. A disulfide bond with Cys65 rather than Cys66 was inferred by homology with Torpedo acetylcholinesterase. Cys571 forms a disulfide bridge with Cys571 of an identical subunit. This interchain disulfide bridge is four amino acids from the carboxyl terminus. A peptide containing the interchain disulfide is readily cleaved from cholinesterase by trypsin (Lockridge, O., and La Du, B. N. (1982) J. Biol. Chem. 257, 12012-12018), suggesting that the carboxyl terminus is near the surface of the globular tetrameric protein. The disulfide bridges in human cholinesterase have exactly the same location as in Torpedo californica acetylcholinesterase. There is one potential free sulfhydryl in human cholinesterase at Cys66, but this sulfhydryl could not be alkylated. Comparison of human cholinesterase, and Torpedo and Drosophila acetylcholinesterases to the serine proteases suggests that the cholinesterases constitute a separate family of serine esterases, distinct from the trypsin family and from subtilisin.
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PMID:Location of disulfide bonds within the sequence of human serum cholinesterase. 311 73

Two enzymes, alkaline phosphatase and acetylcholinesterase (AChE), have been shown previously to be components of the surface of the trematode parasite Schistosoma mansoni. In this study we report that both these enzymes and other serine hydrolases are susceptible to release from the S. mansoni tegumental membrane by a phosphatidylinositol-specific phospholipase C (PIPLC) of bacterial origin. These data suggest that AChE and alkaline phosphatase of S. mansoni, as in higher organisms, are anchored to the membrane via covalently attached phosphatidylinositol. The release of AChE from the vesicular fraction of the parasite with PIPLC occurs in a concentration-dependent manner. Sucrose gradient centrifugation of the PIPLC-released AChE showed a single 8.3 S molecular form, similar to that observed for AChE solubilized by Triton X-100. PIPLC removed large amounts of AChE from the surface of intact schistosomula in culture, with no impairment of the viability of the parasite. In this case, an increase in the overall levels of AChE in the intact parasite was observed after addition of PIPLC.
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PMID:Acetylcholinesterase in Schistosoma mansoni is anchored to the membrane via covalently attached phosphatidylinositol. 313 66

The structural profile for the interactions between serine proteases and organophosphorus (OP) compounds can be deduced from recent NMR and X-ray crystallographic data. Using the rationale proposed for serine proteases, dynamic data on the inhibition of acetylcholinesterase by OP compounds is also consistent with structural constraints and an impairment of the proton switch mechanism during phosphorylation.
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PMID:Structure and dynamics of serine hydrolase-organophosphate adducts. 324 Nov 81

A comparison of the lipid content of normal and carrier-erythrocytes from cattle revealed no differences in phosphatidyl ethanolamine, sphingomyelin, phosphatidyl serine, or cholesterol. The ratio of membrane phospholipid to cholesterol and membrane-bound erythrocyte acetyl cholinesterase activity was unchanged. A microcytic tendency was observed for carrier-cells, however, this physical property of the cell cannot be related to measurable differences in lipid content of the cells.
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PMID:A comparison of membrane lipid content of normal and carrier-erythrocytes from cattle. 324 85

The 60-kDa esterase was isolated from liver microsomes of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced rabbits and its complete amino acid sequence determined. Automated sequence analysis of intact protein, as well as characterization of the peptides obtained from enzymatic and chemical cleavages, led to the elucidation of the primary structure. The protein is a single polypeptide consisting of 539 residues and molecular weight 59,478. The active site serine is 195, and another diisopropylphospho binding site is at histidyl 441. Carbohydrate chains are attached at aspariginyl residues 61 and 363. Although 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment induces this esterase severalfold, the amino acid sequence of the induced enzyme is identical to that of the enzyme isolated from liver microsomes of untreated rabbits. The sequence of the microsomal esterase is 30% identical with the sequences of human serum cholinesterase and the acetylcholinesterase from Torpedo californica. There is also a close homology between the 60-kDa esterase and the COOH-terminal domain of bovine thyroglobulin.
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PMID:Complete covalent structure of 60-kDa esterase isolated from 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced rabbit liver microsomes. 334 53

In addition to its ability to hydrolyze acetylcholine, purified eel acetylcholinesterase possesses a trypsin-like endopeptidase activity. The tryptic activity is associated with a serine residue at a site that is distinct from the esteratic site. To label both the esteratic and tryptic sites, the enzyme was incubated with the serine hydrolase inhibitor [3H]diisopropyl fluorophosphate. This compound labelled the protein in a biphasic manner, with both slow and rapid labelling kinetics. The time course of the rapid phase was similar to the time course of inactivation of the esteratic activity. The time course of the slow phase was similar to the time course of inactivation of the tryptic activity. Labelling of the nonesteratic site was inhibited by the trypsin inhibitor N alpha-p-tosyl-L-lysine chloromethyl ketone. The total number of sites labelled by [3H]diisopropyl fluorophosphate on eel acetylcholinesterase was 2.6 mol/280,000 g protein, whereas the number of tryptic sites was less (0.52 mol/280,000 g). The results suggest that a subpopulation of acetylcholinesterase molecules may possess tryptic activity. Extensive chromatography of the purified enzyme by ion-exchange and gel filtration failed to separate the labelled tryptic component from acetylcholinesterase. On sodium dodecyl sulfate-polyacrylamide gels, the labelled tryptic component comigrated with a polypeptide of 50,000 molecular weight, which is a major proteolytic digestion product derived from the intact acetylcholinesterase monomer. Because of its localization in many noncholinergic peptide-containing cells, acetylcholinesterase could act as a neuropeptide processing enzyme in these cells.
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PMID:Identification of a trypsin-like site associated with acetylcholinesterase by affinity labelling with [3H]diisopropyl fluorophosphate. 337 13

A cDNA encoding acetylcholinesterase (AChE) (EC 3.1.1.7) from Torpedo californica was isolated and from its nucleotide sequence the entire amino acid sequence of the processed protein and a portion of the leader peptide has been deduced. Approximately 70% of the tryptic peptides from the catalytic subunit of the 11 S form have been sequenced, and a comparison of the peptide sequences with the sequence inferred from the cDNA suggests that the cDNA sequence derives from mRNA for the 11 S form of the enzyme. The amino acid sequence is preceded by a hydrophobic leader peptide and contains an open reading frame encoding for 575 amino acids characteristic of a secreted globular protein. Eight cysteines, most of which are disulfide linked, are found along with four potential sites of N-linked glycosylation. The active-site serine is located at residue 200. Local homology is found with other serine hydrolases in the vicinity of the active site, but the enzyme shows striking global homology with the COOH-terminal portion of thyroglobulin. Further comparison of the amino acid sequences of the individual enzyme forms with other cDNA clones that have been isolated should resolve the molecular basis for polymorphism of the AChE species.
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PMID:Primary structure of acetylcholinesterase: implications for regulation and function. 353 98

The complete amino acid sequence of human serum cholinesterase (choline esterase II (unspecific), EC 3.1.1.8) was determined by Edman degradation of purified peptides. The protein contains 574 amino acids per subunit and nine carbohydrate chains attached to 9 asparagines. The four subunits of cholinesterase appear to be identical. The active site serine is the 198th residue from the amino terminus. The sequence of human serum cholinesterase is 53.8% identical with the sequence of acetylcholinesterase from Torpedo californica and 28% identical with the carboxyl-terminal portion of bovine thyroglobulin.
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PMID:Complete amino acid sequence of human serum cholinesterase. 354 89

Rats injected with a nonlethal acute dose (100 micrograms/kg, sc) of soman (pinacolyl methylphosphonofluoridate) exhibited signs of anticholinesterase toxicity beginning at 5-15 min with increasing severity and lasting for 4-6 hr. Generalized tremors and seizure activity indicated comparatively greater involvement of the central cholinergic system than peripheral neuromuscular effects. During peak toxicity, all the brain regions tested showed more than 95% inhibition of acetylcholinesterase (AChE) activity. The cortex area was maximally affected (99% inhibition). Among skeletal muscles, soleus AChE was most severely affected (94%) and extensor digitorum longus (EDL) the least (72%). Inhibition of EDL AChE occurred at a much slower rate than in brain and other muscles. Significant recovery of AChE activity was seen by 48-72 hr after soman treatment in both brain and skeletal muscles. By Day 7, recovery was virtually complete in skeletal muscles but not in brain, although significant recovery had occurred by this time. Muscle fiber necrosis developed within 6 hr in the soleus and diaphragm, while no necrotic fibers were found in the EDL. The 16 S AChE molecular form showed the fastest recovery of the AChE isozymes in all three muscles. Full recovery was seen after 7 days in soleus and was increased to greater than control activity in diaphragm and EDL. The inhibition pattern of butyrylcholinesterase (BuChE) activity was similar to that described for AChE activity, but the recovery was comparatively faster. Carboxylesterase activity in plasma was decreased to less than 10% of control within 1 hr and recovered to 53% of control within 24 hr. No significant inhibition was seen in hepatic carboxylesterase activity. It can be concluded that soman-induced acute toxicity is directly related to the rate and degree of AChE inhibition. A significant amount of soman binds to non-AChE enzymes with serine sites such as BuChE and carboxylesterases.
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PMID:Biochemical and histochemical alterations following acute soman intoxication in the rat. 356 14


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