Epoxide hydrolase 3 (ABHD9, EH3, EPHX3) is a protein that in humans is encoded by the EPHX3 gene. It is the third defined isozyme in a set of epoxide hydrolase isozymes, the epoxide hydrolases. This set includes the Microsomal epoxide hydrolase (also termed epoxide hydrolase 1, EPHX1, mEH, and EH1); the epoxide hydrolase 2 (also termed soluble epoxide hydrolase, EPHX2, sEH and EH2); and the far less well defined enzymatically, epoxide hydrolase 4 (also termed ABHD7 and EH4). All four enzyme contain an Alpha/beta hydrolase fold suggesting that they have Hydrolysis activity. EH1, EH2, and EH3 have been shown to have such activity in that they add water to epoxides of unsaturated fatty acids to form vicinal cis (see cis-trans isomerism) products; the activity of EH4 has not been reported. The former three EH's differ in subcellular location, tissue expression patterns, substrate preferences, and thereby functions. These functions include limiting the biologically actions of certain fatty acid epoxides, increasing the toxicity of other fatty acid epoxides, and contributing to the metabolism of drugs and other xenobiotics.
