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An arti®cial peroxidase-like hemoprotein has been obtained by associating a monoclonal antibody, 13G10, and its iron(III)±a,a,a,b-meso-tetrakis(ortho-carboxyphenyl)por-phyrin [Fe(ToCPP)] hapten. In this antibody, about two-thirds of the porphyrinmoiety is inserted in the binding site, its ortho-COOH substituents being recognized by amino-acids of the protein, and a carboxylic acid side chain of the protein acts as a general acid base catalyst in the heterolytic cleavage of the O±O bond of H2O2, but no amino-acid res-idue is actingas anaxial ligandof the iron | Eur. J. Biochem. 269 470-480 2002 FEBS 2002 Coordination chemistry of iron III porphyrin antibody complexes Influence on the peroxidase activity of the axial coordination of an imidazole on the iron atom Solange de Lauzon1 Daniel Mansuy1 and Jean-Pierre Mahy2 1 Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques UMR 8601 CNRS Universite Rene Descartes Paris France 2Laboratoire de Chimie Bioorganique et Bioinorganique FRE 2127 CNRS ICMO Bat. 420 Universite Paris-Sud XI Orsay France An artificial peroxidase-like hemoprotein has been obtained by associating a monoclonal antibody 13G10 and its iron III -a a a P-meso-tetrakis ortho-carboxyphenyl por-phyrin Fe ToCPP hapten. In this antibody about two-thirds of the porphyrin moiety is inserted in the binding site its ortho-COOH substituents being recognized by aminoacids of the protein and a carboxylic acid side chain of the protein acts as a general acid base catalyst in the heterolytic cleavage of the O-O bond of H2O2 but no amino-acid residue is acting as an axial ligand of the iron.We here show that the iron of 13G10-Fe ToCPP is able to bind like that of free Fe ToCPP two small ligands such as CN- but only one imidazole ligand in contrast to to the iron III of Fe ToCPP that binds two. This phenomenon is general for a series of monosubstituted imidazoles the 2- and 4-alkyl-substituted imidazoles being the best ligands in agreement with the hydrophobic character of the antibody binding site. Complexes of antibody 13G10 with less hindered iron III -tetraarylporphyrins bearing only one Fe MoCPP or two meso- ortho-carboxyphenyl substituents Fe DoCPP also bind only one imidazole. Finally peroxidase activity studies show that imidazole inhibits the peroxidase activity of 13G10-Fe ToCPP whereas it increases that of 13G10-Fe DoCPP . This could be interpreted by the binding of the imidazole ligand on the iron atom which probably occurs in the case of 13G10-Fe ToCPP on the less hindered face of the porphyrin .
