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
K
m
= 21 ± 0.3 μM,
V
Max
= 338 ± 12 nmol⋅min
−1
⋅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.
基因EPXH2编码可溶性环氧酯酶(sEH),这是一种参与心血管和肾脏生理调节的酶,包含两个不同的结构域,通过富含脯氨酸的连接器相连。C端包含EH催化活性的结构域已经得到了广泛的研究。相比之下,N端结构域的功能,其与脱卤酸酶家族的磷酸酶具有高度同源性,尚未被明确报告。在本研究中,我们将N端结构域描述为一种功能性磷酸酶,不受多种经典磷酸酶抑制剂的影响。假设这些催化活性之间存在功能关联,那么二羟基脂肪酸磷酸酯就被合理地解释为潜在的内源性底物。因此,一系列磷酸化羟基脂肪酸被合成,并发现它们是人类sEH的优良底物。最佳的底物是二羟基硬脂酸的单磷酸盐(threo-9/10-磷酸氧基-羟基十八酸),其Km = 21±0.3μM,Vmax = 338±12nmol⋅min^-1⋅mg^-1,kcat = 0.35±0.01s^-1。因此,二羟基脂肪酸磷酸酯是sEH N端结构域的可能内源性底物,这将代表一种具有潜在信号功能的脂肪酸代谢新分支。