Hydrogen sulfide (H[sub]2S) is generated in mammalian tissues from homocysteine and cysteine catalyzed by cystathionine a-synthase and cystathionine c-lyase, the key enzymes of the transsulfuration
pathway of methionine metabolism.
2004); in response, homocysteine is permanently removed from the methionine cycle through degradation into cysteine in the transsulfuration
cycle, where it is converted to cysteine and then to glutathione, a universal antioxidant (Schmidt and LaSalle 2011).
Cystathionine was generated by transmethylation in the process of Met metabolism , and then cystathionine transsulfuration
produced cysteine , and cysteine finally transformed into taurine , which plays important roles in antioxidant .
S-adenosylmethionine (SAM): Common co-substrate involved in methyl group transfers, transsulfuration
, and aminopropylation.
Its metabolism is at the intersection of two metabolic pathways: Remethylation and transsulfuration
Homocysteine is metabolized in the body by either the transsulfuration
or remethylation pathways.
The second step of this pathway involves the transsulfuration
pathway, which converts homocysteine to cysteine and other products.
Miller, "The pathogenesis of homocysteinemia: interruption of the coordinate regulation by S-adenosylmethionine of the remethylation and transsulfuration
of homocysteine," The American Journal of Clinical Nutrition, vol.
Park, "Involvement of hydrogen sulfide and homocysteine transsulfuration
pathway in the progression of kidney fibrosis after ureteral obstruction," Biochimica et Biophysica Acta-Molecular Basis of Disease, vol.
25) Homocysteine is converted to cystathionine to form cysteine via transsulfuration
pathway, which is facilitated by two pyridoxal phosphate dependent enzymes, cystathionine synthase and cystathionase.
2]S biogenesis via alternative transsulfuration
Third, the transsulfuration
pathway from homocysteine to cystathionine which is catalyzed by cystathionine beta synthase (CBS) is tightly related to the methylation pathway.