The vinyl-sulfonium bond in human myeloperoxidase: impact on compound I formation and reduction by halides and thiocyanate.

In human myeloperoxidase (MPO) the heme is covalently attached to the protein via two ester linkages and a unique sulfonium ion linkage between the sulfur atom of Met243 and the beta-carbon of the vinyl ring on pyrrole ring A. Here, we have investigated the variant Met243Val produced in Chinese hamster ovary cells in order to elucidate the role of the electron withdrawing sulfonium bond in compound I formation and reduction. Disruption of this MPO-typical bond causes a blue-shifted UV-vis spectrum and an increase in the heme flexibility.