The enzyme cysteine lyase (EC 4.4.1.10)
catalyzes
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
the
chemical reaction
:
L-cysteine + sulfite
L-cysteate + hydrogen sulfide
This enzyme belongs to the family of
lyase
In biochemistry, a lyase is an enzyme that catalyzes the breaking (an elimination reaction) of various chemical bonds by means other than hydrolysis (a substitution reaction) and oxidation, often forming a new double bond or a new ring structure. ...
s, specifically the class of carbon-sulfur lyases. The
systematic name of this enzyme class is
L-cysteine hydrogen-sulfide-lyase (adding sulfite;
L-cysteate-forming). Other names in common use include cysteine (sulfite) lyase, and
L-cysteine hydrogen-sulfide-lyase (adding sulfite). This enzyme participates in
cysteine
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile.
When present as a deprotonated catalytic residue, sometime ...
and
taurine metabolism. It employs one
cofactor,
pyridoxal phosphate.
Evolution
Genes encoding cysteine lyase (CL) originated around 300 million years ago by a tandem
gene duplication
Gene duplication (or chromosomal duplication or gene amplification) is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene. ...
and
neofunctionalization of
cystathionine β-lyase (CBS) shortly after the split of mammalian and reptilian lineages. CL genes are found only in ''
Sauropsida
Sauropsida ("lizard faces") is a clade of amniotes, broadly equivalent to the class Reptilia. Sauropsida is the sister taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early syna ...
'' where they are involved in a metabolic pathway for
sulfur metabolism in the chicken egg.
References
EC 4.4.1
Pyridoxal phosphate enzymes
Enzymes of unknown structure
{{lyase-stub