Acetylcholinesterase: Theory of noncompetitive inhibition

Froede, Harry C.; Wilson, Irwin B.; Kaufman, H.

doi:10.1016/0003-9861(86)90601-6

Cited by 15 publications

(11 citation statements)

References 7 publications

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“…The role of the peripheral anionic site in AChE function is still unclear. Substrate inhibition of AChE at high ACh concentrations is well documented (Augustinsson, 1948;Quinn, 1987) and it has been proposed that it occurs directly at the active center (Froede et al, 1986) or indirectly through a peripheral site which changes the active center allosterically (Changeux, 1966;Rosenberry, 1975). Recent kinetic studies (Radic et al, 1991) using propidium, a ligand selective for the peripheral anionic site, suggest that the binding site for substrate inhibition and the peripheral anionic site may consist of the same or overlapping structural elements.…”

Section: Introductionmentioning

confidence: 99%

Substrate inhibition of acetylcholinesterase: residues affecting signal transduction from the surface to the catalytic center.

et al. 1992

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Amino acids located within and around the ‘active site gorge’ of human acetylcholinesterase (AChE) were substituted. Replacement of W86 yielded inactive enzyme molecules, consistent with its proposed involvement in binding of the choline moiety in the active center. A decrease in affinity to propidium and a concomitant loss of substrate inhibition was observed in D74G, D74N, D74K and W286A mutants, supporting the idea that the site for substrate inhibition and the peripheral anionic site overlap. Mutations of amino acids neighboring the active center (E202, Y337 and F338) resulted in a decrease in the catalytic and the apparent bimolecular rate constants. A decrease in affinity to edrophonium was observed in D74, E202, Y337 and to a lesser extent in F338 and Y341 mutants. E202, Y337 and Y341 mutants were not inhibited efficiently by high substrate concentrations. We propose that binding of acetylcholine, on the surface of AChE, may trigger sequence of conformational changes extending from the peripheral anionic site through W286 to D74, at the entrance of the ‘gorge’, and down to the catalytic center (through Y341 to F338 and Y337). These changes, especially in Y337, could block the entrance/exit of the catalytic center and reduce the catalytic efficiency of AChE.

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Section: Introductionmentioning

confidence: 99%

Substrate inhibition of acetylcholinesterase: residues affecting signal transduction from the surface to the catalytic center.

et al. 1992

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“…site or a central one. Although the substrate inhibition had been proposed to be due to the binding of acetylcholine to the active centre of AChE [1,7], more recent studies suggest that the binding site for substrate inhibition may be a peripheral anionic site [8,9]. There exist two classes of inhibitors ofAChE activity; one class covers the structurally diverse cationic organic compounds interacting with the active centre [1,10,11] and the other includes ligands associable with a peripheral site remote from the active centre [12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Multiple binding sites involved in the effect of choline esters on decarbamoylation of monomethylcarbamoyl- or dimethylcarbamoly-acetylcholinesterase

Sok

Kim

Choi

et al. 1994

Biochemical Journal

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Multiple binding sites for inhibitory choline esters in spontaneous decarbamoylation of dimethylcarbamoyl-acetylcholinesterase (AChE) were suggested from a wide range of IC50 values, in contrast with a limited range of AC50 values (concentration giving 50% of maximal activation) at a peripheral activatory site. Association of choline esters containing a long acyl chain (C7-C12) with the hydrophobic zone in the active site could be deduced from a linear relationship between the size of the acyl group and the inhibitory potency in either spontaneous decarbamoylation or acetylthiocholine hydrolysis. Direct support for laurylcholine binding to the active site might come from the competitive inhibition (Ki 33 microM) of choline-catalysed decarbamoylation by laurylcholine. Moreover, its inhibitory action was greater for monomethylcarbamoyl-AChE than for dimethylcarbamoyl-AChE, where there is a greater steric hindrance at the active centre. In further support, the inhibition of pentanoylthiocholine-induced decarbamoylation by laurylcholine was suggested to be due to laurylcholine binding to a central site rather than a peripheral site, similar to the inhibition of spontaneous decarbamoylation by laurylcholine. Supportive data for acetylcholine binding to the active site are provided by the results that acetylcholine is a competitive inhibitor (Ki 7.6 mM) of choline-catalysed decarbamoylation, and its inhibitory action was greater for monomethylcarbamoyl-AChE than for dimethylcarbamoyl-AChE. Meanwhile, choline esters with an acyl group of an intermediate size (C4-C6), more subject to steric exclusion at the active centre, and less associable with the hydrophobic zone, appear to bind preferentially to a peripheral activity site. Thus the multiple effects of choline esters may be governed by hydrophobicity and/or a steric effect exerted by the acyl moiety at the binding sites.

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“…[72] (obtained with ATCh and AChE from E. electricus), who reported K I = 20.4 nm and K I * = a¢K I (1 + k 3 ⁄ k 2 ) = 38.3 nm for tacrine on the basis of the kinetic model in Scheme 3 (with b = 0)[72,73]. For comparison, we calculated a¢ = 1.1 using these values ofK I and K I *.…”

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Kinetics of inhibition of acetylcholinesterase in the presence of acetonitrile

et al. 2009

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Acetylcholinesterase (AChE, EC 3.1.1.7) is a serine hydrolase [1], which belongs to the a ⁄ b hydrolase family [2,3]. The enzyme hydrolyses a broad range of ester and amide substrates, showing the highest specificity for acetylselenocholine, acetylthiocholine (ATCh) and acetylcholine (ACh) [4]. Substrate cleavage proceeds via a two-step mechanism: acylation of the enzyme, followed by deacylation involving a water molecule [5][6][7]. This process is mediated by the catalytic triad Ser200-His440-Glu327 (Torpedo californica AChE, TcAChE, numbering [8]) located within the active site at the bottom of a 20 Å deep gorge. Substrate binding is facilitated by another component of the active site, the anionic site, which is characterized by several conserved aromatic residues, such as Trp84 and Phe330. These residues have been shown to interact with the quaternary ammonium groups of ACh or ATCh via cation-p interactions [7][8][9][10][11][12]. Further stabilization of the quaternary moiety arises from an electrostatic interaction with the acidic side-chain of Glu199 [7,12]. A second substrate-binding site, the peripheral anionic site (PAS), lies essentially on the The hydrolysis of acetylthiocholine by acetylcholinesterase from Electrophorus electricus was investigated in the presence of the inhibitors tacrine, gallamine and compound 1. The interaction of the enzyme with the substrate and the inhibitors was characterized by the parameters K I , a¢, b or b, K m and V max , which were determined directly and simultaneously from nonlinear Michaelis-Menten plots. Tacrine was shown to act as a mixedtype inhibitor with a strong noncompetitive component (a¢ % 1) and to completely block deacylation of the acyl-enzyme. In contrast, acetylcholinesterase inhibition by gallamine followed the 'steric blockade hypothesis', i.e. only substrate association to as well as substrate ⁄ product dissociation from the active site were reduced in the presence of the inhibitor. The relative efficiency of the acetylcholinesterase-gallamine complex for the catalysis of substrate conversion was determined to be 1.7-25% of that of the free enzyme. Substrate hydrolysis and the inhibition of acetylcholinesterase were also investigated in the presence of 6% acetonitrile, and a competitive pseudo-inhibition was observed for acetonitrile (K I = 0.25 m). The interaction of acetylcholinesterase with acetonitrile and tacrine or gallamine resulted in a seven-to 10-fold increase in the K I values, whereas the principal mode of inhibition was not affected by the organic solvent. The determination of the inhibitory parameters of compound 1 in the presence of acetonitrile revealed that the substance acts as a hyperbolic mixed-type inhibitor of acetylcholinesterase. The complex formed by the enzyme and the inhibitor still catalysed product formation with 8.7-9.6% relative efficiency.

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Acetylcholinesterase: Theory of noncompetitive inhibition

Cited by 15 publications

References 7 publications

Substrate inhibition of acetylcholinesterase: residues affecting signal transduction from the surface to the catalytic center.

Substrate inhibition of acetylcholinesterase: residues affecting signal transduction from the surface to the catalytic center.

Multiple binding sites involved in the effect of choline esters on decarbamoylation of monomethylcarbamoyl- or dimethylcarbamoly-acetylcholinesterase

Kinetics of inhibition of acetylcholinesterase in the presence of acetonitrile

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