Artificial peroxidase-like hemoproteins based on antibodies constructed from a specifically designed ortho-carboxy substituted tetraarylporphyrin hapten and exhibiting a high affinity for iron-porphyrins

Abstract

In order to get catalytic antibodies modelling peroxidases BALB/c mice have been immunized with iron(III)α,α,α,β- mesotetrakis-orthocarboxyphenyl-porphyrin (Fe(ToCPP))-KLH conjugates. Monoclonal antibodies have been produced by the hybridoma technology. Three antibodies, 2 IgG, and 1 IgG 2a, were found to bind both Fe(ToCPP) and the free base ToCPPH 2 with similar binding constants. None of those antibodies was found to bind tetraphenylporphyrin. Those results suggest that the recognition of Fe(ToCPP) by the antibodies was mainly due to the binding of the carboxylate groups to some amino acid residues of the protein. True K d values of 2.9 × 10 −9 M and 5.5 × 10 −9 M have been determined for the two IgG 1-Fe(ToCPP) complexes. Those values are the best ones ever reported for iron-porphyrin-antibody complexes. UV-vis. studies have shown that the two IgG 1-Fe(ToCPP) complexes were highspin hexacoordinate iron(III) complexes, with no amino acid residue binding the iron, whereas the IgG 2α-Fe(ToCPP) complex was a low-spin hexacoordinate iron(III) complex with two strong ligands binding the iron atom. Both IgG 1 -Fe(ToCPP) complexes were found to catalyze the oxidation of 2,2′-azinobis (3ethylbenzothiazoline-6-sulfonic acid (ABTS) 5-fold more efficiently than Fe(ToCPP) alone whereas the binding of IgG 2a to this iron-porphyrin had no effect on its catalytic activity. k cat values of 100 min −1 and 63 min −1 and k cat/ K m. values of 105 M −1 s −1 and 119 M −1 s −1 have been found respectively for the two IgG 1-Fe(ToCPP) complexes.