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.
+ L-Cysteine consumption pathways 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 acidglutamate–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.
+ L-cysteine production pathwaysReactants→Enzyme CofactorsNotesO-acetyl-L-serine/hydrogen sulfide→cysteine synthase pyridoxal phosphatenot present in humansL-cystine/2 glutathione→glutathione-cystine transhydrogenasecystathionine→cystathionine γ-lyase pyridoxal phosphate3-mercapto-pyruvate→cysteine transaminasepyridoxal phosphate
References
See also D-cysteine desulfhydrase Sulfur metabolism