Cystathionine
Encyclopedia
Cystathionine is an intermediate in the synthesis of cysteine
.
It is generated from homocysteine
and serine by cystathionine beta synthase
.
It is cleaved into cysteine
and α-ketobutyrate by cystathionine gamma-lyase
.
An excess in the urine is called cystathioninuria
.
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
.
It is generated from homocysteine
Homocysteine
Homocysteine is a non-protein amino acid with the formula HSCH2CH2CHCO2H. It is a homologue of the amino acid cysteine, differing by an additional methylene group. It is biosynthesized from methionine by the removal of its terminal Cε methyl group...
and serine by cystathionine beta synthase
Cystathionine beta synthase
Cystathionine-β-synthase, also known as CBS, is an enzyme that in humans is encoded by the CBS gene. It catalyzes the first step of the transsulfuration pathway, from homocysteine to cystathionine:...
.
It is cleaved into cysteine
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
and α-ketobutyrate by cystathionine gamma-lyase
Cystathionine gamma-lyase
Cystathionine gamma-lyase is an enzyme which breaks down cystathionine into cysteine and α-ketobutyrate. Pyridoxal phosphate is a prosthetic group of this enzyme....
.
An excess in the urine is called cystathioninuria
Cystathioninuria
Cystathioninuria, also called cystathionase deficiency, is an autosomal recessive metabolic disorder that results in an excess of cystathionine in the urine. It is associated with a congenital dysfunction of the enzyme cystathionase, or acquired deficiency of vitamin B6 which is essential for the...
.