In the general context of green chemistry, a considerable research effort is devoted to the elaboration of new artificial metalloproteins that catalyze, under mild conditions, the oxidation of a wide range of organic compounds, using cheap and environmentally friendly oxidants. A new artificial hemoprotein was obtained by the so-called Trojan horse" strategy involving the non-covalent insertion of a cationic iron-porphyrin-estradiol cofactor into an anti-estradiol antibody. UV-vis titrations showed the formation of a 1/2 antibody/cofactor complex with a dissociation constant K-D = 4.10(-7) M. UV-vis determination of the Fe-imidazole binding constants showed that the protein provided a weak steric hindrance around the iron-porphyrin cofactor. The antibody-estradiol-iron-prophyrin complex displayed a peroxidase activity and catalyzed the oxidation of ABTS by H2O2 with about double the efficiency of the iron-porphyrin-estradiol alone. Kinetic studies revealed that this was due to a faster formation of the intermediate high valent iron-oxo species in the presence of the antibody protein. Consequently, the association of an anti-estradiol antibody with an iron-porphyrin-estradiol cofactor leads to a new artificial hemoprotein with an interesting peroxidase activity and the "Trojan horse" strategy appears as a valuable method to generate artificial metalloenzymes that could act as biocatalysts for selective oxidations. (C) 2009 Elsevier B.V. All rights reserved.