The effects of thioureylene compounds (goitrogens) on lactoperoxidase activity

The rates of oxidation of several goitrogens by lactoperoxidase and the rates of inactivation of lactoperoxidase by the same goitrogens have been measured. The influence of iodide on both reactions has also been evaluated. It has been shown by us that iodide acts catalytically in regulating lactoperoxidase activity at pH 8.8. The rate data have been analyzed by a computer program which solves the differential equations for the above mentioned reactions. From this computer analysis we have been able to obtain binding constants of the goitrogens and inactivation rate constants of lactoperoxidase. Iodide was shown to inhibit goitrogenic activity either by increasing the rate of drug oxidation or by reducing the rate of enzyme inactivation, or both, depending on the particular drug. Iodide had little or no effect on the goitrogen-binding constants. We have also shown that the relative rates of enzyme inactivation can be correlated with the potency of the goitrogen as an antithyroid drug.