Ross Matthew K, Pluta Kim, Bittles Victoria, Borazjani Abdolsamad, Allen Crow J
Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762, United States; Center for Environmental Health Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762, United States.
Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762, United States.
Arch Biochem Biophys. 2016 Jan 15;590:72-81. doi: 10.1016/j.abb.2015.11.034. Epub 2015 Nov 23.
Oxons are bioactive metabolites of organophosphorus insecticides (OPs) that covalently inactivate serine hydrolases. KIAA1363 is one of the most abundant serine hydrolases in mouse brain. Although the physiological consequences related to the inhibition of KIAA1363 due to environmental exposures to OPs are poorly understood, the enzyme was previously shown to have a role in the detoxification of oxons. Here, we overexpressed human KIAA1363 and CES1 in COS7 cells and compared the potency of inhibition (IC50s, 15 min) of KIAA1363 and CES1 by chlorpyrifos oxon (CPO), paraoxon (PO), and methyl paraoxon (MPO). The order of potency was CPO > PO >> MPO for both enzymes. We also determined the bimolecular rate constants (kinact/Ki) for reactions of CPO and PO with KIAA1363 and CES1. KIAA1363 and CES1 were inactivated by CPO at comparable rates (4.4 × 10(6) s(-1) M(-1) and 6.7 × 10(6) s(-1) M(-1), respectively), whereas PO inactivated both enzymes at slower rates (0.4 × 10(6) s(-1) M(-1) and 1.5 × 10(6) s(-1) M(-1), respectively). Finally, the reactivation rate of KIAA1363 following inhibition by CPO was evaluated. Together, the results define the kinetics of inhibition of KIAA1363 by active metabolites of agrochemicals and indicate that KIAA1363 is highly sensitive to inhibition by these compounds.
氧磷是有机磷杀虫剂（OPs）的生物活性代谢产物，可共价失活丝氨酸水解酶。KIAA1363是小鼠脑中含量最丰富的丝氨酸水解酶之一。尽管由于环境暴露于OPs而抑制KIAA1363所产生的生理后果尚不清楚，但先前已证明该酶在氧磷的解毒中起作用。在这里，我们在COS7细胞中过表达人KIAA1363和CES1，并比较了毒死蜱氧磷（CPO）、对氧磷（PO）和甲基对氧磷（MPO）对KIAA1363和CES1的抑制效力（IC50，15分钟）。两种酶的效力顺序均为CPO＞PO＞＞MPO。我们还测定了CPO和PO与KIAA1363和CES1反应的双分子速率常数（kinact/Ki）。CPO使KIAA1363和CES1失活的速率相当（分别为4.4×10⁶ s⁻¹ M⁻¹和6.7×10⁶ s⁻¹ M⁻¹），而PO使两种酶失活的速率较慢（分别为0.4×10⁶ s⁻¹ M⁻¹和1.5×10⁶ s⁻¹ M⁻¹）。最后，评估了CPO抑制后KIAA1363的重新激活速率。总之，这些结果确定了农用化学品活性代谢产物对KIAA1363的抑制动力学，并表明KIAA1363对这些化合物的抑制高度敏感。
