Amitai G, Moorad D, Adani R, Doctor B P
Division of Biochemistry, Walter Reed Army Institute of Research, Washington, DC 20307-5100, USA.
Biochem Pharmacol. 1998 Aug 1;56(3):293-9. doi: 10.1016/s0006-2952(98)00035-5.
Phosphorothionate insecticides such as parathion (O,O-diethyl O-p-nitrophenyl phosphorothioate) and chlorpyrifos (CPS; O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate; Dursban) are metabolically converted by oxidative desulfuration into paraoxon and chlorpyrifos-oxon (CPO). The insecticidal action of chlorpyrifos stems from inhibition of acetylcholinesterase (AChE) by CPO, resulting in severe cholinergic toxicity. Sensory peripheral neuropathy was observed in people exposed environmentally to chlorpyrifos sprayed in confined areas. We have examined the kinetics of inhibition of AChE and butyrylcholinesterase (BChE) by paraoxon and CPO. The bimolecular rate constants (ki) for inhibition by paraoxon of recombinant human (rH) AChE, recombinant mouse (rM) AChE, and fetal bovine serum (FBS) AChE were 7.0, 4.0, and 3.2 x 10(5) M(-1) min(-1). The ki values for the inhibition by CPO of rH AChE, fetal bovine serum AChE, human RBC AChE, Torpedo AChE, and recombinant mouse (rM) AChE were 9.3, 2.2, 3.8, 8.0, and 5.1 x 10(6) M(-1) min(-1), respectively. Inhibition of human serum BChE, rH BChE, and rM BChE by CPO yielded ki values of 1.65, 1.67, and 0.78 x 10(9) M(-1) min(-1), respectively. The ki values obtained for BChE from various species were 160- to 750-fold larger than those of AChE from parallel sources. Inhibition of the single-site mutant A328Y of rH BChE by CPO displayed a 21-fold lower rate than that of wild-type rH BChE (ki, 7.9 x 10(7) vs 1.67 x 10(9) M(-1) min(-1)). The double mutant of acyl pocket residues of rH AChE, F295L/F297V, was inhibited by CPO with a 150-fold larger ki than wild type (1.5 x 10(9) vs 1.0 x 10(7) M(-1) min(-1)). The increased rate obtained with the double mutant displaying characteristics of the BChE active center provides a rationale for higher efficacy of CPO scavenging by BChE, compared with AChE.
硫代磷酸酯类杀虫剂，如对硫磷（O,O - 二乙基 - O - 对硝基苯基硫代磷酸酯）和毒死蜱（CPS；O,O - 二乙基 - O - 3,5,6 - 三氯 - 2 - 吡啶基硫代磷酸酯；敌百虫），通过氧化脱硫代谢转化为对氧磷和毒死蜱 - 氧磷（CPO）。毒死蜱的杀虫作用源于CPO对乙酰胆碱酯酶（AChE）的抑制，导致严重的胆碱能毒性。在密闭区域接触环境中喷洒的毒死蜱的人群中观察到感觉性周围神经病变。我们研究了对氧磷和CPO对AChE和丁酰胆碱酯酶（BChE）的抑制动力学。对氧磷对重组人（rH）AChE、重组小鼠（rM）AChE和胎牛血清（FBS）AChE的抑制双分子速率常数（ki）分别为7.0、4.0和3.2×10⁵ M⁻¹ min⁻¹。CPO对rH AChE、胎牛血清AChE、人红细胞AChE、电鳐AChE和重组小鼠（rM）AChE的抑制ki值分别为9.3、2.2、3.8、8.0和5.1×10⁶ M⁻¹ min⁻¹。CPO对人血清BChE、rH BChE和rM BChE的抑制产生的ki值分别为1.65、1.67和0.78×10⁹ M⁻¹ min⁻¹。从各种物种获得的BChE的ki值比来自平行来源的AChE的ki值大160至750倍。CPO对rH BChE的单点突变体A328Y的抑制速率比野生型rH BChE低21倍（ki，7.9×10⁷对1.67×10⁹ M⁻¹ min⁻¹）。rH AChE的酰基口袋残基的双突变体F295L/F297V被CPO抑制时，其ki值比野生型大150倍（1.5×10⁹对1.0×10⁷ M⁻¹ min⁻¹）。具有BChE活性中心特征的双突变体获得的速率增加为BChE清除CPO的效率高于AChE提供了理论依据。
