Effects of Ionizing Radiation on Arylesterase and Cholinesterase.

Augustinsson, Klas‐Bertil; Jonsson, Gunnel; Sparrman, Berndt; Nielsen, G. Bech; Nord, H.; Jart, Aage

doi:10.3891/acta.chem.scand.15-0011

Cited by 27 publications

(27 citation statements)

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“…These enzymes can also be distinguished by inhibitor specificity. In addition, the butyrylcholinesterases do not exhibit substrate inhibition characteristic of AChEs (12).…”

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confidence: 94%

“…Subsequent primary structures showed that the cholinesterases belong to a distinct, but functionally eclectic, family of serine hydrolases. Included in this family are the butyrylcholinesterases, hepatic microsomal carboxylesterases, the Drosophila Est-6, lysophospholipases, cholesterol esterases, and two proteins found in inclusion bodies of Dictyostelium (5)(6)(7)(8)(9)(10)(11) (2,12). These enzymes can also be distinguished by inhibitor specificity.…”

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confidence: 99%

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Mutagenesis of essential functional residues in acetylcholinesterase.

Gibney

Camp

Dionne

et al. 1990

Proc. Natl. Acad. Sci. U.S.A.

131

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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 assignnment 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 ofa 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 substrateinhibition 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.Efficiently catalyzed hydrolysis of the neurotransmitter acetylcholine is critical to proper functioning of the cholinergic nervous system, and several pharmacologic and toxicologic agents act by inhibiting acetylcholinesterase (AChE; acetylcholine acetylhydrolase, EC 3.1.1.7). AChE functions as a serine hydrolase (1-3) and enzyme inhibitors used clinically or as insecticides typically serve as alternative substrates by acylating the active-center serine with slower leaving groups. The primary structure of AChE revealed that it lacks global sequence similarities with serine hydrolases of the trypsin and subtilisin families and only possesses residue identity with trypsin immediately around the active-center serine (4). Surprisingly, AChE is homologous to the carboxyl-terminal domain of a large secreted glycoprotein, thyroglobulin, the precursor to thyroid hormone (4). Subsequent primary structures showed that the cholinesterases belong to a distinct, but functionally eclectic, family of serine hydrolases. Included in this family are the butyrylcholinesterases, hepatic microsomal carboxylesterases, the Drosophila Est-6, lysophospholipases, cholesterol esterases, and two proteins found in inclusion bodies of Dictyostelium (5-11).The cholinesterases are characterized by their specificity for choline esters but can be subdivided on the basis of acyl group selectivity. The true AChEs (EC 3.1.1.7) show weak catalytic activity for choline esters with acyl groups larger than propionylcholine; the butyrylcholinesterases (EC 3.1.1.8) efficiently hydrolyze esters with large...

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“…These enzymes can also be distinguished by inhibitor specificity. In addition, the butyrylcholinesterases do not exhibit substrate inhibition characteristic of AChEs (12).…”

mentioning

confidence: 94%

mentioning

confidence: 99%

Mutagenesis of essential functional residues in acetylcholinesterase.

Gibney

Camp

Dionne

et al. 1990

Proc. Natl. Acad. Sci. U.S.A.

131

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“…This distribution of acetylcholinesterase and buty rylcholinesterase may influence the hydrolysis of endogenously released acetylcholine which is mostly inactivated by acetylcholinesterase. Eserine inhibits both the butyryl cholinesterase and acetylcholinesterase (15) and gives complete protection to endogenously released acetylcholine; This causes greater accumulation of acetylcholine in the bath when eserine is used (Table 1). Prostigmine has similar but less anticholinesterase activity than eserine.…”

Section: Discussionmentioning

confidence: 99%

Effect of Cholinesterase Inhibitors and Pam on the Release of Acetylcholine From Isolated Guineapig Ileum

Matin

Kar

1971

Jpn.J.Pharmacol

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Eserine and mipafox have often been used as anticholinesterases to allow measure ment of spontaneous release of acetylcholine from the ileum (1-4). Mipafox was chosen because of its apparent inability to release acetylcholine from smooth muscle (5). It has also been reported that values for acetylcholine release in the presence of mipafox (1) were much lower than those obtained by other workers using eserine (2, 3). It, therefore, fol lows that the choice of a particular anticholinesterase may influence the release of acetyl choline from smooth muscle. In order to experimentally test this possibility, we examined the effect of four cholinesterase inhibitors—eserine, prostigmine, phosphamidon and mipa fox, on the spontaneous release of acetylcholine from isolated guineapig ileum.
P AM (2-pyridyl-aldoxime methiodide) reactivates the phosphorylated (inhibited) cholinesterase (6, 7); At certain concentrations, it induces the release of acetylcholine while at others, it inhibits the acetylcholine release from rat phrenic nerve diaphragm prepara tion (8). The effect of PAM on the release of acetylcholine from smooth muscle has so far not been studied. The effect of PAM, if any, on the acetylcholine output from isolat ed guineapig ileum, in the presence of anticholinesterases, has also been examined in the present study. METHODSGuineapigs (300-400 g) were killed by a blow on the neck and bled. The ileum was taken out, emptied of its contents and divided into several equal pieces. Two pieces, 3 4 cm long, from different parts of the intestine were combined into one sample to reduce the effect of the variations in choline acetylase content (9) along the length of the intestine.The pieces were tied off at both ends to prevent the mucus in the lumen from oozing into the bath fluid. The preparation was set up in the usual way in a 10 ml organ bath con taining Tyrode solution at 37°C with a resting tension of I g. The preparation was wash ed twice at 10 minutes intervals before exposure to any drug. The preparation was next bathed in Tyrode containing the cholinesterase inhibitor for 30 minutes, the bath fluid being changed at 10 minute intervals; At the end of next 15 minutes, the bath fluid was withdrawn for the assay of acetylcholine. In another series of experiments, PAM was added in the bath 15 minutes before the collection of test sample.The biological assay for acetylcholine was made on a fresh piece of isolated guinea

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“…Sodium fluoride is known to cause cholinesterases inhibition [1][2][3][4][5][6][7][8][9][10]. The effect of fluoride concentration on the enzyme activity in vitro and in vivo has been studied by several authors [3,4,7,9,11] and related to the toxic levels of this compound.…”

Section: Introductionmentioning

confidence: 99%