Two steps from serine: activate the hydroxyl with an acetyl group, then swap it for sulfur
Route: Serine + Acetyl-CoA → O-Acetylserine → Cysteine
This is the route in bacteria and plants. Serine acetyltransferase moves the acetyl group from acetyl-CoA onto the hydroxyl of serine. A second enzyme, which needs pyridoxal phosphate, replaces the acetate with sulfide to make cysteine. The sulfide comes from the reduction of sulfate. Humans make cysteine another way, by combining serine with homocysteine from methionine.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Serine acetyltransferase | 2.3.1.30 | CoA-SH | |
| 2 | O-Acetylserine sulfhydrylase | 2.5.1.47 | Hâ‚‚S | Acetate |
Enzyme names and EC numbers are those used on the interactive board. Checked against sources: see the claim table in the repository (tools/pathway_data/checks).