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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.

[edit] 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/CoA biosynthesis.

L-cysteine consumption pathways

enzyme	→	product
cysteine dioxygenase	→	3-sulfino-L-alanine (or cysteine sulfinic acid)
amino-acid racemase	→	D-cysteine
cysteine lyase	→	L-cysteate
cysteine—tRNA ligase	→	L-cysteinyl-tRNACys
cystine reductase	→	L-cystine
cysteine transaminase	→	3-mercapto-pyruvate

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

starting chemical	→	enzyme
O-acetyl-L-serine	→	cysteine synthase
L-cystine	→	glutathione-cystine transhydrogenase
pyruvate	→	cystathionine γ-lyase
3-mercapto-pyruvate	→	cysteine transaminase

[edit] See also

• D-cysteine desulfhydrase
• Sulphur metabolism