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The complex of iron(III) coproporphyrinI (FeCPI) with antibody D5E3 was studied as an artificial peroxidase, using o-dianisidine as a substrate. At saturation with respect to antibody, the initial rates of o-dianisidine oxidation are practically the same for free and bound FeCPI at a concentration 5 x 10(-9)M, but the catalytic rate constant (kc) for bound FeCPI exceed (kc) for free FeCPI by two- to three-fold. This difference can be explained by a real enhancement of (kc) at the antibody-active site. The dependence of initial rates of the reaction on substrate concentrations obeyed Michaelis-Menten kinetics and revealed substrate activation at high concentrations of o-dianisidine. A comparison of the Stern-Volmer constants for o-dianisidine-induced quenching of the porphyrin fluorescence proves that antibody-bound coproporphyrin is equivalently accessible to the substrate as protoporphyrin bound to apoperoxidase from horseradish peroxidase (HRP). Based on analysis of the (kc) dependence on H2O2 concentrations in the FeCPI-antibody system, we suggest that interaction with hydrogen peroxide is the rate-limiting step for the oxidation reaction.

Ah&setMonoclonal antibodies against Pd-coproporphyrin I have been obtained. The antibody specificity for free as well as for conjugated Pd-coproporphyrin I is characterized. Affinity constants are estimated for 3 monoclonal antibodies effectively interacting with free Pd-coproporphyrin I. A comparative study on the binding of monoclonal antibodies with analogues and derivatives of Pd-coproporphyrin I has revealed that the antigen is mainly located inside the antibody paratope. The protein adjoins complementary to the metalloporphyrin in such a manner that antibodies obtained discern only isomer I, and to some degree, isomer III of coproporphyrin.

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