Cysteine

Cysteine ​​is a non-essential amino acid that, like methionine, has a sulfur atom in its molecule.

Metabolism cysteine
Cysteine ​​synthesis takes place in the human organism from homocysteine ​​and serine.

The degradation of cysteine ​​begins with the oxidation of the -SH group to -SO2- by the enzyme cysteine ​​dioxygenase. In the resulting L-cysteine ​​sulfinate, the -NH 2 group is replaced by a keto group with the help of transaminase , and β-sulfinylpyruvate is formed. In the final reaction, it is split by desulfinase into pyruvate and sulfite (SO3-), or final sulfate (SO4-). Cysteine ​​is an important source of taurine. L-cysteine ​​sulfinate is decarboxylated to hypotaurine and subsequent oxidation of the -SO2- - group to -SO3- produces taurine.

Alternative non-oxidative degradation of cysteine ​​produces pyruvate and sulfane (H2S).

Importance

 * In peptides, cysteine ​​is essential for the formation of disulfide bridges.
 * It is a substrate for glutathione.
 * It is a substrate for taurine. The latter is conjugated with bile acids or other substances that increase their solubility in water.
 * Decarboxylation of cysteine ​​produces cysteamine, which is part of coenzyme A.
 * It has a high proportion of keratin protein (hair, nails).

Related articles

 * Amino acids