Cysteine biosynthesis from homoserine (WP256)

Saccharomyces cerevisiae

O-Acetyl-L-homoserine sulfhydrylase participates in an alternative pathway of L-homocysteine synthesis. Cysteine can then be produced by the reverse transsulfuration pathway, which involves the conversion of homocysteine to cysteine with the help of a cystathionine intermediate. This process takes place in two steps: First, cystathionine-synthase (Cys4p) catalyzes a -displacement reaction, whereby the thiol group of homocysteine replaces the hydroxyl group of serine, resulting in the formation of cystathionine. Second, cystathionine-lyase (Cys3p) catalyzes an ,-elimination reaction, which hydrolyzes cystathionine to generate cysteine, -ketobutyrate, and ammonia.


Meredith Braymer , Egon Willighagen , Martina Summer-Kutmon , Susan Coort , Denise Slenter , Alex Pico , and Eric Weitz


last edited

Discuss this pathway

Check for ongoing discussions or start your own.

Cited In

Are you planning to include this pathway in your next publication? See How to Cite and add a link here to your paper once it's online.


Saccharomyces cerevisiae



Pathway Ontology

cysteine metabolic pathway


Label Type Compact URI Comment
homocysteine Metabolite cas:6027-13-0
cystathionine Metabolite cas:56-88-2
L-cysteine Metabolite cas:52-90-4
acetate Metabolite cas:64-19-7
2-oxobutanoate Metabolite hmdb:HMDB0000005
NH3 Metabolite hmdb:HMDB0000051
homoserine Metabolite cas:672-15-1
acetyl-CoA Metabolite cas:72-89-9
L-serine Metabolite cas:56-45-1
Coenzyme A Metabolite cas:64885-97-8
CYS4 GeneProduct sgd:S000003387
MET17 GeneProduct sgd:S000004294
MET2 GeneProduct sgd:S000005221
CYS3 GeneProduct sgd:S000000010