Fig. 1.

Established vascular phenotypes associated with transsulfuration. Cystathionine β-synthase (CBS) is the first enzyme of the transsulfuration pathway and has the unique property of the nonreversible catabolism of homocysteine. Hydrogen sulfide (H₂S) is produced during transsulfuration by both CBS and cystathionine γ-lyase (CGL). CBS activity determines the balance between the vascular damage of hyperhomocysteinemia and the protective potential of endogenous H₂S production. CGL has the capacity to metabolize homocysteine in vitro (dashed line from homocysteine to CGL).