Is Novel Signal Transducer Sulfur Oxide Involved in the Redox Cycle of Persulfide at the Catalytic Site Cysteine in a Stable Reaction Intermediate of Mercaptopyruvate Sulfurtransferase

Abstract In transsulfuration reaction catalyzed by rat mercaptopyruvate sulfurtransferase (MST), a stable persulfide is formed at the catalytic site cysteine Cys247 as a reaction intermediate. The outer sulfur atom is donated by the substrate, thiosulfate, or by mercaptopyruvate. MST serves as a thioredoxin-dependent antioxidant possessing self-regulated enzymatic activity. After oxidation of persulfurated MST by treatment with hydrogen peroxide, mass spectrometric analysis showed that the outer sulfur atom of the persulfide is oxidized to form Cys-thiosulfenate (Cys-Sγ-SO−), Cys-thiosulfinate (Cys-Sγ-SO2−), and Cys-thiosulfonate (Cys-Sγ-SO3−). Next, sulfur acceptor substrates including reduced thioredoxin convert all modified cysteines to nonmodified cysteines. Another sulfur acceptor substrate, cyanide, also converted these cysteines via cyanolysis. Thus, sulfur oxides are suggested to release in the redox cycle of persulfide of MST. Antioxid. Redox Signal. 16, 747–753.