Mahy, J.-P.

Eur. J. Biochem. 1998, 257, 121-130, 10.1046/j.1432-1327.1998.2570121.x

The topology of the binding site has been studied for two monoclonal antibodies 13G10 and 14H7, elicited against iron(III)‐α,α,α,β‐meso‐tetrakis(ortho‐carboxyphenyl)porphyrin {α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin]}, and which exhibit in the presence of this α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin] cofactor a peroxidase activity. A comparison of the dissociation constants of the complexes of 13G10 and 14H7 with various tetra‐aryl‐substituted porphyrin has shown that : (a) the central iron(III) atom of α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin] is not recognized by either of the two antibodies; and (b) the ortho‐carboxylate substituents of the meso‐phenyl rings of α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin] are essential for the recognition of the porphyrin by 13G10 and 14H7. Measurement of the dissociation constants for the complexes of 13G10 and 14H7 with the four atropoisomers of (o‐COOHPh)4‐porphyrinH2 as well as mono‐ and di‐ortho‐carboxyphenyl‐substituted porphyrins suggests that the three carboxylates in the α, α, β position are recognized by both 13G10 and 14H7 with the two in the α, β positions more strongly bound to the antibody protein. Accordingly, the topology of the active site of 13G10 and 14H7 has roughly two‐thirds of the α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin] cofactor inserted into the binding site of the antibodies, with one of the aryl ring remaining outside. Three of the carboxylates are bound to the protein but no amino acid residue acts as an axial ligand to the iron atom. Chemical modification of lysine, histidine, tryptophan and arginine residues has shown that only modification of arginine residues causes a decrease in both the binding of α,α,α,β‐Fe[(o‐COOHPh)4‐porphyrin] and the peroxidase activity of both antibodies. Consequently, at least one of the carboxylates of the hapten is bound to an arginine residue and no amino acids such as lysine, histidine or tryptophan participate in the catalysis of the heterolytic cleavage of the O‐O bond of H2O2. In addition, the amino acid sequence of both antibodies not only reveals the presence of arginine residues, which could be those involved in the binding of the carboxylates of the hapten, but also the presence of several amino acids in the complementary determining regions which could bind other carboxylates through a network of H bonds.

Sheldon, R.A.

Chem. Commun. 1998, 1891-1892, 10.1039/a804702b

Phytase (E.C. 3.1.3.8), which in vivo mediates the hydrolysis of phosphate esters, catalyses the enantioselective oxidation of thioanisole with H2O2, both in the presence and absence of vanadate ion, affording the S-sulfoxide in up to 66% ee at 100% conversion.

Mahy, J.-P.

Appl. Biochem. Biotechnol. 1998, 75, 103-127, 10.1007/Bf02787712

Besides existing models of chemical or biotechnological origin for hemoproteins like peroxidases and cytochromes P450, catalytic antibod ies (Abs) with a metalloporphyrin cofactor represent a promising alter native route to catalysts tailored for selective oxidation reactions. A brief overview of the literature shows that, until now, the first strategy for obtaining such artificial hemoproteins has been to produce antipor phyrin Abs, raised against various free-base, N-substituted, Sn-,Pd-,or Fe-porphyrins. Four of them exhibited, in the presence of the corre sponding Fe-porphyrin cofactor, a significant peroxidase activity, with kcat/Km values of 102 to 5 × 103/M/s. This value remained low when com pared to that of peroxidases, probably because neither a proximal ligand of the Fe, nor amino acid residues participating in the catalysis of the heterolytic cleavage of the O—O bond of H2O2, have been induced in those Abs. This strategy has been shown to be insufficient for the elabo ration of effective models of cytochromes P450, because only one set of Abs, raised againstmeso-tetrakis(para-carboxyvinylphenyl)porphyrin, was reported to catalyze the nonstereoselective oxidation of styrene by iodosyl benzene using a Mn-porphyrin cofactor, and attempts to gener ate Abs having binding sites for both the substrate and the metallopor phyrin cofactor, using as a hapten a porphyrin covalently linked to the substrate, were not successful. A second strategy is then proposed, which involves the chemical labeling of antisubstrate Abs with a metallopor phyrin. As an example, preliminary results are presented on the covalent linkage of an Fe-porphyrin to an antiestradiol Ab, in order to obtain semisynthetic catalytic Abs able to catalyze the selective oxidation of steroids.