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.

Human cysteine metabolism

In human cysteine metabolism, L-cysteine is consumed in several ways as shown below. L-Cysteine is also consumed in pantothenate/coenzyme A biosynthesis.
Enzyme→ProductsCofactor/Additional Reactant
cysteine dioxygenase→cysteine sulfinic acidiron
serine racemase→D-cysteinepyridoxal phosphate
cysteine lyase→L-cysteate/hydrogen sulfidepyridoxal phosphate/sulfite
cystathionine γ-lyase→pyruvate/NH3/H2Spyridoxal phosphate
cysteine—tRNA ligase→L-cysteinyl-tRNACys
cystine reductase→L-cystine/NADH and H+NAD+
cysteine transaminase→3-mercapto-pyruvate/L-glutamatepyridoxal phosphate/alpha-ketoglutaric acid
glutamate–cysteine ligase→γ-glutamyl cysteine/ADP and PiATP

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→EnzymeCofactorsNotes
O-acetyl-L-serine/hydrogen sulfide→cysteine synthasepyridoxal phosphatenot present in humans
L-cystine/2 glutathione→glutathione-cystine transhydrogenase
cystathionine→cystathionine γ-lyasepyridoxal phosphate
3-mercapto-pyruvate→cysteine transaminasepyridoxal phosphate