Simultaneous and sensitive quantification of protein and low molecular weight persulfides, polysulfides and H(2)S in biological samples.

H(2)S reversibly modifies low molecular weight (L(MW)SH) and protein (PrSH) thiols to form persulfides (RSS(-)) and polysulfides (RS(S)(n)S(-)) for antioxidant defence and regulation of activity. However, our understanding of the biological significance of these processes is hampered by our inability to quantify these modifications. We develop a sensitive LC-MS/MS procedure that traps the sulfur atom of H(2)S, and the terminal sulfur atom of RSS(-) and RS(S)(n)S(-) as diagnostic products in biological samples. In parallel, we also trap internal S atoms of RS(S)(n)S(-), enabling quantification of H(2)S, RSS(-) and RS(S)(n)S(-). L(MW)S(S)(n)S(-) and PrS(S)(n)S(-) are determined simultaneously in the same sample. Glutathione (GSH) is the most abundant L(MW)SH so we develop an orthogonal approach to quantify GSS(-), enabling corroboration of L(MW)SS(-) measurements by sulfur atom trapping. We demonstrate in systems from proteins to ex vivo tissues how these approaches enable exploration of persulfidation in biological systems.