Mechanism-based inhibition of lactoperoxidase by thiocarbamide goitrogens.

The irreversible inactivation of bovine lactoperoxidase by thiocarbamide goitrogens was measured, and the kinetics were consistent with a mechanism-based (suicide) mode. Sulfide ion inactivated, 2-mercaptobenzimidazole-inactivated, and 1-methyl-2-mercaptoimidazole-inactivated lactoperoxidases have different visible spectra, suggesting different products were formed. The results support a mechanism in which reactive intermediates are formed by S-oxygenation reactions catalyzed by lactoperoxidase compound II. It is proposed that the reaction of electron-deficient intermediates with the heme prosthetic group is responsible for the observed spectral changes and inactivation by thiocarbamides.