Biochemical and kinetic characterization of wild type and pathogenic mutant forms of human ETHE1

Abstract

Hydrogen sulfide (H2S) is a recently described gaseous signaling molecule, which influences various cellular processes involving the central nervous system, cardiovascular system as well as mitochondrial energy metabolism. H2S is produced endogenously from the desulfhydration of cysteine and homocysteine by the enzymes of the transsulfuration pathway. Understanding the regulation of steady‐state H2S levels awaits biochemical characterization of the enzymes responsible for the oxidation and metabolic removal of H2S, sulfide quinone oxidoreductase, sulfur dioxygenase (ETHE1) and a sulfurtransferase. Mutations in the persulfide oxidizing enzymes, i.e. ETHE1, result in ethylmalonic encephalopathy, an autosomal recessive disorder. In this study, we report the biochemical characterization and kinetic properties of ETHE1 and describe the deficiencies associated with two patient mutations, T152I and D196N. Steady‐state kinetic analysis shows that T152I mutation results in 3‐fold lower activity, which is correlated with a 3‐fold lower iron content compared to wild‐type enzyme. The D196N mutation results in a 2‐fold higher Km for the substrate, glutathione persulfate (GSSH).