In enzymology, a cysteine transaminase (EC 2.6.1.3) is an enzyme that catalyzes the chemical reaction

L-cysteine + 2-oxoglutarate ${\displaystyle \rightleftharpoons }$ mercaptopyruvate + L-glutamate

Thus, the two substrates of this enzyme are L-cysteine and 2-oxoglutarate, whereas its two products are mercaptopyruvate and L-glutamate.

This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-cysteine:2-oxoglutarate aminotransferase. Other names in common use include cysteine aminotransferase, L-cysteine aminotransferase, and CGT. This enzyme participates in cysteine metabolism. It employs one cofactor, pyridoxal phosphate.