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,^{[citation needed]} 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	→	Products	Cofactor/Additional Reactant
cysteine dioxygenase^[1]	→	cysteine sulfinic acid	iron
serine racemase^[2]	→	D-cysteine	pyridoxal phosphate
cysteine lyase^[3]	→	L-cysteate/hydrogen sulfide	pyridoxal phosphate/sulfite
cystathionine γ-lyase^[4]	→	pyruvate/NH₃/H₂S	pyridoxal phosphate
cysteine—tRNA ligase^[5]	→	L-cysteinyl-tRNA^Cys
cystine reductase^[6]	→	L-cystine/NADH and H+	NAD+
cysteine transaminase^[7]	→	3-mercapto-pyruvate/L-glutamate	pyridoxal phosphate/alpha-ketoglutaric acid
glutamate–cysteine ligase^[8]	→	γ-glutamyl cysteine/ADP and P_i	ATP

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 pathways**
Reactants	→	Enzyme	Cofactors	Notes
O-acetyl-L-serine/hydrogen sulfide	→	cysteine synthase^[9]	pyridoxal phosphate	not present in humans
L-cystine/2 glutathione	→	glutathione-cystine transhydrogenase^[10]
cystathionine	→	cystathionine γ-lyase^[4]	pyridoxal phosphate
3-mercapto-pyruvate	→	cysteine transaminase^[7]	pyridoxal phosphate

Cysteine metabolism

Human cysteine metabolism

References

See also