Reactions of ferryl lactoperoxidase (compound II) with sulfide and sulfhydryl compounds

Lactoperoxidase in the ferryl state (compound II) reacts with sulfide to form a typical sulfheme -containing hemoprotein as do hemoglobin, myoglobin, and catalase. Ferrous sulflactoperoxidase is primarily formed and then oxidized to its ferric form under aerobic conditions. Similar reactions of lactoperoxidase occurs when methylmercaptoimidazole (MMI) is substituted for sulfide. The yield of the adducts from one-turnover reactions of ferryl lactoperoxidase is 100% with sulfide and about 20% with MMI. Sulfur and MMI of the adducts appear to be removed from the enzyme upon reduction by dithionite. Upon the reactions with cysteine and dithiothreitol, the enzyme is converted to spectral species, which are less characteristic but are similar to ferrous and ferric sulflactoperoxidases , respectively. We conclude that there is no essential difference in the mechanism of reactions of lactoperoxidase with sulfide, MMI, cysteine, and dithiothreitol.