Sulfheme proteins. IV. The stoichiometry of sulfur incorporation and the isolation of sulfhemin, the prosthetic group of sulfmyoglobin.

The ferrous form of sulfmyoglobin was isolated as the first stable product of the reaction of a single mole of inorganic sulfide with 1 mole of the higher oxidation state derivative of myoglobin, Mb’“. Using radioactive sulfide, it was demonstrated that a single g atom of sulfur is incorporated per mole of myoglobin to form sulfmyoglobin. More than 85% of the radioactive sulfur is extracted into 2-butanone at pH 3.2, bound to the prosthetic group of sulfmyoglobin. The optical properties of the prosthetic group, which we call “sulfhemin,” and of some of its derivatives have been studied. Sulfhemin is unstable in organic solvents in the presence of O2 or peroxides and decomposes to yield protohemin in an autoxidative reaction which follows first order kinetics. Sulfate is the major sulfur compound ultimately produced in the decomposition of sulfhemin. Mercuric ion was also found to cause the decomposition of sulfhemin.