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-9/ 10-phosphonoxy-hydroxy-octadecanoic acid) with Km = 21 ± 0.3 μM, VMax = 338 ± 12 nmol·min-1·mg-1, and kcat = 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.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Feb 18 2003|
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