Cohen S D, Williams R A, Killinger J M, Freudenthal R I
Toxicol Appl Pharmacol. 1985 Dec;81(3 Pt 1):452-9. doi: 10.1016/0041-008x(85)90416-8.
Biochemical studies were conducted to compare the in vitro sensitivities of bovine and rodent brain and erythrocyte cholinesterases to inhibition by Dyfonate-oxon, paraoxon, and malaoxon. This comparison was done to determine if the reported greater sensitivity of cattle to Dyfonate might be explained by a greater sensitivity of the target enzyme, acetylcholinesterase, in cattle to inhibition by Dyfonate's toxic metabolite, Dyfonate-oxon. Studies were conducted with brain homogenates and lysed erythrocytes obtained from cows and from male and female rats. Additional studies were conducted with a commercially available sample of purified bovine erythrocyte acetylcholinesterase (ACHE). In all cases, the concentrations of organophosphates required to produce 50% inhibition (IC50) of enzyme activity were determined. Cow brain ACHE was 1.7 to 3.8 times more resistant to inhibition by Dyfonate-oxon, paraoxon, and malaoxon than was brain ACHE from male or female rats. For both species, paraoxon was 1.2 to 1.6 times more potent than Dyfonate-oxon and 3.8 to 6.9 times more potent than malaoxon. The bimolecular reaction rate constants (ki) were also determined for inhibition of brain ACHE of cows and male rats by the three organophosphates. In general, the ki data were in agreement with the IC50 data indicating that cow brain ACHE was less sensitive than rat brain ACHE to inhibition. Additional IC50 studies were conducted with lysed erythrocytes from cows and from male and female rats. Both quantitative and qualitative differences between species and among the organophosphates were in excellent agreement with the results of the brain ACHE studies. Also, in related studies with purified bovine erythrocyte ACHE, there was excellent agreement with the results of tests involving ACHE inhibition in erythrocyte lysates. This study demonstrated that, as an inhibitor of ACHE in vitro, Dyfonate-oxon was equal to or slightly lower in potency than paraoxon and more potent than malaoxon. In addition, the study demonstrated that, in general, ACHE from brain or erythrocytes of cows was less sensitive to in vitro inhibition by organophosphates than was that from male or female rats. Thus, the apparent greater susceptibility of cows to Dyfonate, in vivo, cannot be explained on the basis of an unusual target enzyme (ACHE) sensitivity to inhibition by Dyfonate-oxon.
进行了生化研究，以比较牛和啮齿动物的脑及红细胞胆碱酯酶对敌匹硫磷 - 氧磷、对氧磷和马拉氧磷抑制作用的体外敏感性。进行这种比较是为了确定所报道的牛对敌匹硫磷更高的敏感性是否可以用牛体内目标酶乙酰胆碱酯酶对敌匹硫磷有毒代谢物敌匹硫磷 - 氧磷抑制作用的更高敏感性来解释。研究使用了从奶牛以及雄性和雌性大鼠获得的脑匀浆和裂解红细胞。还对市售的纯化牛红细胞乙酰胆碱酯酶（ACHE）样本进行了研究。在所有情况下，均测定了产生50%酶活性抑制（IC50）所需的有机磷酸酯浓度。牛脑ACHE对敌匹硫磷 - 氧磷、对氧磷和马拉氧磷抑制作用的抗性比雄性或雌性大鼠脑ACHE高1.7至3.8倍。对于这两个物种，对氧磷的效力比对氧磷高1.2至1.6倍，比对马拉氧磷高3.8至6.9倍。还测定了三种有机磷酸酯对奶牛和雄性大鼠脑ACHE抑制作用的双分子反应速率常数（ki）。总体而言，ki数据与IC50数据一致，表明牛脑ACHE比对大鼠脑ACHE的抑制敏感性更低。对奶牛以及雄性和雌性大鼠的裂解红细胞进行了额外的IC50研究。物种之间以及有机磷酸酯之间的定量和定性差异与脑ACHE研究结果高度一致。此外，在对纯化牛红细胞ACHE的相关研究中，与涉及红细胞裂解物中ACHE抑制的测试结果高度一致。这项研究表明，作为体外ACHE的抑制剂，敌匹硫磷 - 氧磷的效力等于或略低于对氧磷，且比对马拉氧磷更有效。此外，该研究表明，总体而言，来自奶牛脑或红细胞的ACHE比对雄性或雌性大鼠的ACHE对体外有机磷酸酯抑制作用的敏感性更低。因此，牛在体内对敌匹硫磷明显更高的易感性不能基于目标酶（ACHE）对敌匹硫磷 - 氧磷抑制作用的异常敏感性来解释。
