5-nitro-2-mercaptobenzimidazole and 2-mercaptobenzimidazole

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.

Topics: Animals; Benzimidazoles; Cattle; Imidazoles; Kinetics; Lactoperoxidase; Methimazole; Peroxidases; Protein Binding; Spectrophotometry; Structure-Activity Relationship