Oxygenation of organosulfur compounds by peroxidases: evidence of an electron transfer mechanism for lactoperoxidase.

The oxygenation of benzyl methylsulfide, thioanisole, and thiobenzamide to the respective sulfoxides was found to be catalyzed by chloroperoxidase, lactoperoxidase, and horseradish peroxidase. The activities of lactoperoxidase and horseradish peroxidase were similarly low toward benzyl methylsulfide and thioanisole but lactoperoxidase efficiently catalyzed the oxygenation of thiobenzamide while horseradish peroxidase showed low activity. Chloroperoxidase had high reactivity toward all three substrates tested in halide-independent reactions and only small differences in the rates of enzymatic sulfoxidation were observed. The logarithm of lactoperoxidase activity was found to linearly correlate with the voltammetric peak potentials for oxidation of the three substrates tested. The results of this study are consistent with a one-electron transfer mechanism for lactoperoxidase-mediated sulfoxidation.