Reaction: PXLP-CBS tetramers condenses HCYS and L-Ser to form L-Cystathionine
- in pathway: Cysteine formation from homocysteine
The first step of homocysteine conversion to cysteine is catalyzed by cystathionine beta-lyase, which adds a serine molecule to the substrate. The enzyme is a tetramer with two heme molecules as cofactor (Janosik et al. 2001). CBS also utilises pyridoxal 5'-phosphate (PXLP) as cofactor, at the evolutionarily conserved Lys119 residue (Kery et al. 1999). The cystathionine beta-synthase-like protein (CBSL) is thought to function like CBS.
Reaction - small molecule participants:
L-Cystathionine [cytosol]
H2O [cytosol]
L-Ser [cytosol]
HCYS [cytosol]
Reactome.org reaction link: R-HSA-1614524
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Reaction input - small molecules:
L-serine zwitterion
homocysteine zwitterion
Reaction output - small molecules:
L-cystathionine
water
Reactome.org link: R-HSA-1614524