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The poorly known mechanism of inhibition of cholinesterases by inorganic mercury (HgCl2) has been studied with a view to using these enzymes as biomarkers or as biological components of biosensors to survey polluted areas. The inhibition of a variety of cholinesterases by HgCl2 was investi-gated by kinetic studies, X-ray crystallography, and dynamic light scatter-ing. | ỊFEBS Journal Mechanisms of cholinesterase inhibition by inorganic mercury Manuela F. Frasco1 2 Jacques-Philippe Colletier3 Martin Weik3 Felix Carvalho4 Lucia Guilhermino1 2 Jure Stojan5 and Didier Fournier6 1 ICBAS Institute de Ciencias Biomedicas de AbelSalazar Universidade do Porto Portugal 2 CIMAR-LA CIIMAR Universidade do Porto Portugal 3 IBS-UMR 5075 CEA-CNRS-UJF Laboratoire de Biophysique Moleculaire Grenoble France 4 REQUIMTE Servico de Toxicologia da Faculdade de Farmacia da Universidade do Porto Portugal 5 Institute of Biochemistry University of Ljubljana Slovenia 6 IPBS-UMR 5089 CNRS-UPS Groupe de Biotechnologie des Proteines Toulouse France Keywords aggregation cholinesterase inhibition mercury metals Correspondence D. Fournier IPBS-UMR 5089 205 Route de Narbonne F-31077 Toulouse France Fax 33 5 61 17 59 94 Tel 33 5 61 55 54 45 E-mail fournier@ipbs.fr Database The coordinates and structure factor amplitudes of the complex structure of human butyrylcholinesterase with HgCl2 have been deposited in the Protein Data Bank under accession code 2J4C Received 18 December 2006 revised 1 February 2007 accepted 7 February 2007 doi 10.1111 j.1742-4658.2007.05732.x The poorly known mechanism of inhibition of cholinesterases by inorganic mercury HgCl2 has been studied with a view to using these enzymes as biomarkers or as biological components of biosensors to survey polluted areas. The inhibition of a variety of cholinesterases by HgCl2 was investigated by kinetic studies X-ray crystallography and dynamic light scattering. Our results show that when a free sensitive sulfhydryl group is present in the enzyme as in Torpedo californica acetylcholinesterase inhibition is irreversible and follows pseudo-first-order kinetics that are completed within 1 h in the micromolar range. When the free sulfhydryl group is not sensitive to mercury Drosophila melanogaster acetylcholinesterase and human butyrylcholinesterase or is otherwise absent Electrophorus electri-cus .