Assay methods for H2S biogenesis and catabolism enzymes

Abstract

H2S is produced from sulfur-containing amino acids, cysteine and homocysteine, or a catabolite, 3-mercaptopyruvate, by three known enzymes: cystathionine β-synthase, γ-cystathionase, and 3-mercaptopyruvate sulfurtransferase. Of these, the first two enzymes reside in the cytoplasm and comprise the transsulfuration pathway, while the third enzyme is found both in the cytoplasm and in the mitochondrion. The following mitochondrial enzymes oxidize H2S: sulfide quinone oxidoreductase, sulfur dioxygenase, rhodanese, and sulfite oxidase. The products of the sulfide oxidation pathway are thiosulfate and sulfate. Assays for enzymes involved in the production and oxidative clearance of sulfide to thiosulfate are described in this chapter.

Keywords: Cystathionine β-synthase; Hydrogen sulfide; Mercaptopyruvate sulfurtransferase; Rhodanese; Sulfur dioxygenase; γ-Cystathionase.

Figure 1

Scheme showing enzymes involved in H₂S biogenesis and oxidation. For simplicity, H₂S production by MST is shown in the mitochondrion only although the enzyme can be present in the cytoplasm and mitochondrion. CBS, CSE, CAT, MST, and SQR denote cystathionine β-synthase, γ-cystathionase, cysteine aminotransferase, mercaptopyruvate sulfur transferase, and sulfide quinone oxidoreductase, respectively. Electrons from the mitochondrial sulfide oxidation pathway are transferred via ubiquinone to complex III in the electron transfer chain.