Cysteine metabolism


Cysteine metabolism refers to the biological pathways that consume or create cysteine. The pathways of different amino acids and other metabolites interweave and overlap to creating complex systems.cysteine is metabolism creating complex systems

Human cysteine metabolism

In human cysteine metabolism, L-cysteine is consumed in several ways as shown below. L-Cysteine is also consumed in methionine and glutathione metabolism as well as pantothenate/coenzyme A biosynthesis.
EnzymeCofactor/Additional Reactant→Products
cysteine dioxygenaseiron→cysteine sulfinic acid
amino-acid racemasepyridoxal phosphate→D-cysteine
cysteine lyasepyridoxal phosphate/sulfite→L-cysteate/hydrogen sulfide
cystathionine γ-lyasepyridoxal phosphate→NH3/H2S
cysteine—tRNA ligase→L-cysteinyl-tRNACys
cystine reductaseNAD+→L-cystine/NADH and H+
cysteine transaminasepyridoxal phosphate/alpha-ketoglutaric acid→3-mercapto-pyruvate/L-glutamate

L-Cysteine is the product of several processes as well. In addition to the reactions below, L-cysteine is also a product of glycine, serine, and threonine metabolism.
Reactants→EnzymeCofactors
O-acetyl-L-serine/hydrogen sulfide→cysteine synthasePyridoxal phosphate
L-cystine/2 glutathione→glutathione-cystine transhydrogenase
cystathionine→cystathionine γ-lyasepyridoxal phosphate
3-mercapto-pyruvate→cysteine transaminasepyridoxal phosphate