Carboxylesterase 5 (CES5) is a member of a large family of carboxylesterases that are responsible for the hydrolysis of ester and amide bonds. They have broad substrate specificity ranging from small molecule esters such as phenylester to long-chain fatty acid esters and thioesters. Carboxylesterases play a major role as determinants of pharmacokinetic behavior for most therapeutic agents containing an ester, participating in the detoxification of drugs such as cocaine and heroin in serum and liver. They can also detoxify organophosphate and carbamate analogues used in agrochemicals or chemical nerve agents, such as malathion, sarin, tabun, and VX.
Carboxylesterases can also perform transesterification, a reaction important for cholesterol homeostasis. Carboxylesterase deficiency may be associated with non-Hodgkin lymphoma or B-cell lymphocytic leukemia. CES5 shares the serine hydrolase fold observed in other esterases. CES5 possesses an endoplasmic reticulum retention signal (HKEL) at its C-terminus.