Interaction of propylthiouracil and its precursors with horseradish peroxidase.

Interactions of horseradish peroxidase with propylthiouracil, thiouracil, propyluracil and uracil lead to the formation of complexes that exhibit different absorption spectra which can be attributed to the perturbation of peroxidase as the result of the drug-binding on a polar site in the protein. In this paper, by dilatometry and viscometry structural alterations in horseradish peroxidase were detected from its interaction with propylthiouracil and thiouracil only, and the physiological inhibition of peroxidase for these antithyroid drugs seems to be through structural alterations in the protein.