title: The soluble epoxide hydrolase encoded by EPXH2 is a bifunctional enzyme with novel lipid phosphate phosphatase activity.
abstract: The gene EPXH2 encodes for the soluble epoxide hydrolase (sEH), an enzyme involved in the regulation of cardiovascular and renal physiology containing two distinct domains connected via a proline-rich linker. The C-terminal domain containing the EH catalytic activity has been well studied. In contrast, a function for the N-terminal domain, which has high homology to the haloacid dehalogenase family of phosphatases, has not been definitively reported. In this study we describe the N-terminal domain as a functional phosphatase unaffected by a number of classic phosphatase inhibitors. Assuming a functional association between these catalytic activities, dihydroxy lipid phosphates were rationalized as potential endogenous substrates. A series of phosphorylated hydroxy lipids were therefore synthesized and found to be excellent substrates for the human sEH. The best substrate tested was the monophosphate of dihydroxy stearic acid (threo-910-phosphonoxy-hydroxy-octadecanoic acid) with K(m) = 21 +/- 0.3 microM, V(Max) = 338 +/- 12 nmol x min(-1) x mg(-1), and k(cat) = 0.35 +/- 0.01 s(-1). Therefore dihydroxy lipid phosphates are possible candidates for the endogenous substrates of the sEH N-terminal domain, which would represent a novel branch of fatty acid metabolism with potential signaling functions.
authors.affiliation: Department of Entomology and University of California Davis Cancer Center, University of California, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: John W
authors.initials: JW
authors.lastname: Newman
authors.forename: Christophe
authors.initials: C
authors.lastname: Morisseau
authors.forename: Todd R
authors.initials: TR
authors.lastname: Harris
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Hammock
mesh_terms: D004791:Enzyme Inhibitors / Q000494:pharmacology; D004851:Epoxide Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D013058:Mass Spectrometry; D010711:Phosphatidate Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012995:Solubility; D013379:Substrate Specificity
chemical_list: D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; C112948:lipid phosphate phosphatase; D010711:Phosphatidate Phosphatase; D004851:Epoxide Hydrolases; D008274:Magnesium