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 methionine and glutathione metabolism as well as pantothenate/coenzyme A biosynthesis.
| Enzyme | Cofactor/Additional Reactant | → | Products |
|---|---|---|---|
| cysteine dioxygenase | iron | → | cysteine sulfinic acid |
| amino-acid racemase | pyridoxal phosphate | → | D-cysteine |
| cysteine lyase | pyridoxal phosphate/sulfite | → | L-cysteate/hydrogen sulfide |
| cystathionine γ-lyase | pyridoxal phosphate | → | NH3/H2S |
| cysteine—tRNA ligase | → | L-cysteinyl-tRNACys | |
| cystine reductase | NAD+ | → | L-cystine/NADH and H+ |
| cysteine transaminase | pyridoxal phosphate/alpha-ketoglutaric acid | → | 3-mercapto-pyruvate/L-glutamate |
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 | → | Enzyme | Cofactors |
|---|---|---|---|
| O-acetyl-L-serine/hydrogen sulfide | → | cysteine synthase | Pyridoxal phosphate |
| L-cystine/2 glutathione | → | glutathione-cystine transhydrogenase | |
| cystathionine | → | cystathionine γ-lyase | pyridoxal phosphate |
| 3-mercapto-pyruvate | → | cysteine transaminase | pyridoxal phosphate |
See also
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