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