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PMID:14766237

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Citation

Schallreuter, KU, Elwary, SM, Gibbons, NC, Rokos, H and Wood, JM (2004) Activation/deactivation of acetylcholinesterase by H2O2: more evidence for oxidative stress in vitiligo. Biochem. Biophys. Res. Commun. 315:502-8

Abstract

Previously it has been demonstrated that the human epidermis synthesises and degrades acetylcholine and expresses both muscarinic and nicotinic receptors. These cholinergic systems have been implicated in the development of the epidermal calcium gradient and differentiation in normal healthy skin. In vitiligo severe oxidative stress occurs in the epidermis of these patients with accumulation of H2O2 in the 10(-3)M range together with a decrease in catalase expression/activity due to deactivation of the enzyme active site. It was also shown that the entire recycling of the essential cofactor (6R)-l-erythro-5,6,7,8-tetrahydrobiopterin via pterin-4a-carbinolamine dehydratase (PCD) and dihydropteridine reductase (DHPR) is affected by H2O2 oxidation of Trp/Met residues in the enzyme structure leading to deactivation of these proteins. Using fluorescence immunohistochemistry we now show that epidermal H2O2 in vitiligo patients yields also almost absent epidermal acetylcholinesterase (AchE). A kinetic analysis using pure recombinant human AchE revealed that low concentrations of H2O2 (10(-6)M) activate this enzyme by increasing the Vmax>2-fold, meanwhile high concentrations of H2O2 (10(-3)M) inhibit the enzyme with a significant decrease in Vmax. This result was confirmed by fluorescence excitation spectroscopy following the Trp fluorescence at lambdamax 280nm. Molecular modelling based on the established 3D structure of human AchE supported that H2O2-mediated oxidation of Trp(432), Trp(435), and Met(436) moves and disorients the active site His(440) of the enzyme, leading to deactivation of the protein. To our knowledge these results identified for the first time H2O2 regulation of AchE. Moreover, it was shown that H2O2-mediated oxidation of AchE contributes significantly to the well-established oxidative stress in vitiligo.

Links

PubMed Online version:10.1016/j.bbrc.2004.01.082

Keywords

Acetylcholinesterase/chemistry; Acetylcholinesterase/metabolism; Binding Sites; Biopsy; Catalase/biosynthesis; Dihydropteridine Reductase/metabolism; Dose-Response Relationship, Drug; Epidermis/enzymology; Epidermis/metabolism; Humans; Hydro-Lyases/metabolism; Hydrogen Peroxide/chemistry; Hydrogen Peroxide/pharmacology; Immunohistochemistry; Kinetics; Microscopy, Fluorescence; Models, Molecular; Oxidative Stress; Oxygen/metabolism; Skin/metabolism; Spectrometry, Fluorescence; Tryptophan/chemistry; Up-Regulation; Vitiligo/metabolism; Vitiligo/pathology

Significance

Annotations

Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status

HUMAN:ACES

located_in

GO:0048471: perinuclear region of cytoplasm

ECO:0000314: direct assay evidence used in manual assertion

C

Seeded From UniProt

complete

HUMAN:ACES

part_of

GO:0048471: perinuclear region of cytoplasm

ECO:0000314: direct assay evidence used in manual assertion

C

Seeded From UniProt

complete


See also

References

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