Cysteine metabolism

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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.

Human cysteine metabolism[edit]

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.

L-Cysteine consumption pathways
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.

L-cysteine production pathways
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[edit]