Cystathionine gamma-lyase
The enzyme cystathionine γ-lyase (EC 4.4.1.1, CTH or CSE; also cystathionase; systematic name L-cystathionine cysteine-lyase (deaminating; 2-oxobutanoate-forming)) breaks down cystathionine into cysteine, 2-oxobutanoate (α-ketobutyrate), and ammonia:
- L-cystathionine + H2O = L-cysteine + 2-oxobutanoate + NH3 (overall reaction)
- (1a) L-cystathionine = L-cysteine + 2-aminobut-2-enoate
- (1b) 2-aminobut-2-enoate = 2-iminobutanoate (spontaneous)
- (1c) 2-iminobutanoate + H2O = 2-oxobutanoate + NH3 (spontaneous)
| cystathionine γ-lyase | |||||||||
|---|---|---|---|---|---|---|---|---|---|
Cysteine metabolism. Cystathionase catalyzes the lower reaction. | |||||||||
| Identifiers | |||||||||
| EC no. | 4.4.1.1 | ||||||||
| CAS no. | 9012-96-8 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| Gene Ontology | AmiGO / QuickGO | ||||||||
| |||||||||
| cystathionase (cystathionine γ-lyase) | |||||||
|---|---|---|---|---|---|---|---|
| Identifiers | |||||||
| Symbol | CTH | ||||||
| NCBI gene | 1491 | ||||||
| HGNC | 2501 | ||||||
| OMIM | 607657 | ||||||
| RefSeq | NM_001902 | ||||||
| UniProt | P32929 | ||||||
| Other data | |||||||
| EC number | 4.4.1.1 | ||||||
| Locus | Chr. 1 p31.1 | ||||||
| |||||||
Pyridoxal phosphate is a prosthetic group of this enzyme.
Cystathionine γ-lyase also catalyses the following elimination reactions:
- L-homoserine to form H2O, NH3 and 2-oxobutanoate
- L-cystine, producing thiocysteine, pyruvate and NH3
- L-cysteine producing pyruvate, NH3 and H2S
In some bacteria and mammals, including humans, this enzyme takes part in generating hydrogen sulfide. Hydrogen sulfide is one of a few gases that was recently discovered to have a role in cell signaling in the body.
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