Inhibition of human and murine cytosolic epoxide hydrolase by group-selective reagents

1. Human and murine cytosolic epoxide hydrolase were inhibited by thiol-, imidazole- and carboxyl-selective reagents. They were not inhibited by amino-, guanido- or activated serine-selective reagents. 2. Murine, but not human, cytosolic epoxide hydrolase was inhibited by N-bromosuccinimide, a tryptophan selective reagent. 3. Based on sequence data from peptides isolated from CNBr digests, human and murine CEH share areas of sequence homology. Of the five unique human CEH CNBr peptides sequenced, three shared common sequences with one of the unique murine CEH CNBr peptides. The human and murine CEH peptides with common sequences had between 64 and 78% sequence identity. 4. A cysteine important for the activity of murine CEH appears not to be in the active site as judged by N-phenylmaleimide inhibition in the presence and absence of either (2S,3S)-2,3-epoxy-3-(4-nitrophenyl)glycidol, a competitive inhibitor, or trans-stilbene oxide, a substrate.