Hydrogen Sulfide Biochemistry and Interplay with Other Gaseous Mediators in Mammalian Physiology

Figure 1

Hydrogen sulfide biosynthetic pathways in mammalian physiology. (a) Transsulfuration branch of the methionine cycle. L-Methionine (Met) is converted by L-methionine adenosyltransferase to S-adenosyl-L-methionine (AdoMet), which is used by methyltransferases in methylation reactions, generating S-adenosyl-L-homocysteine (AdoHcy). AdoHcy hydrolase then converts AdoHcy into L-homocysteine (Hcy), which can either be converted back to L-methionine through the remethylation cycle ([remet]), or enter the transsulfuration branch. Cystathionine β-synthase (CBS) converts Hcy and L-serine into L-cystathionine (Cysth), which is taken up by cystathionine γ-lyase (CSE) to generate L-cysteine (Cys). Hydrogen sulfide (H₂S) is synthesized by CBS and CSE in several alternative reactions (see Figure 2). (b) H₂S synthesis by 3-mercaptopyruvate sulfurtransferase (MST). Cys is converted by cysteine aminotransferase (CAT) into 3-mercaptopyruvate (3-MP), which is used by MST to synthesize H₂S along with its cosubstrates thioredoxin (Trx), Cys, Hcy, and l-glutathione (GSH).

(a)

(b)