Figure 1.

Endogenous synthesis of H₂S by four pathways. (A) CSE catalyzes the reaction of L–homocysteine to induce the production of H₂S. (B) CBS reacts with L–homocysteine, increasing the generation of L–cystathionine, which is then converted into L–cysteine via CSE, which further produces H₂S. (C) L–cysteine is converted into 3MP by CAT, and 3–MST catalyzes the reaction of 3MP to induce H₂S generation in mitochondria. (D) DAO reacts with D–cysteine to generate 3MP, which then enters mitochondria and serves as a substrate for the production of H₂S. CBS (cystathionine β–synthase); CSE (cystathionine γ–lyase); CAT (cysteine aminotransferase); 3MP (3–mercaptopyruvate); DAO (D–amino acid oxidase); 3–MST (3–mercaptopyruvate sulfurtransferase).