Lyases;
Carbon-sulfur lyases;
Carbon-sulfur lyases (only sub-subclass identified to date)

L-cysteine sulfide-lyase (deaminating; pyruvate-forming)

L-cysteine + H2O = sulfide + NH3 + pyruvate (overall reaction) [RN:R00782];
(1a) L-cysteine = 2-aminoprop-2-enoate + sulfide;
(1b) 2-aminoprop-2-enoate = 2-iminopropanoate (spontaneous);
(1c) 2-iminopropanoate + H2O = pyruvate + NH3 (spontaneous)

R00782

L-cysteine [CPD:C00097];
H2O [CPD:C00001];
2-aminoprop-2-enoate [CPD:C02218];
2-iminopropanoate [CPD:C20904]

The enzyme from the archaeon Methanocaldococcus jannaschii contains a [4Fe-4S] cluster and is specific for L-cysteine (cf. EC 4.4.1.1, cystathionine gamma-lyase). It cleaves a carbon-sulfur bond releasing sulfide and the unstable enamine product 2-aminoprop-2-enoate that tautomerizes to an imine form, which undergoes a hydrolytic deamination to form pyruvate and ammonia. The same reaction can also be catalysed by some pyridoxal-phosphate proteins (cf. EC 4.4.1.1, cystathionine gamma-lyase).

EC 4.4.1.28 created 2014

1  [PMID:15683250]

Tchong SI, Xu H, White RH

L-cysteine desulfidase: an [4Fe-4S] enzyme isolated from Methanocaldococcus jannaschii that catalyzes the breakdown of L-cysteine into pyruvate, ammonia, and sulfide.

Biochemistry 44:1659-70 (2005)
DOI:10.1021/bi0484769

[mja:MJ_1025]