Devonshire A L
Biochem J. 1977 Dec 1;167(3):675-83. doi: 10.1042/bj1670675.
Carboxylesterases from different strains of Myzus persicae were examined to try to understand their contribution to insecticide resistance. Preliminary evidence that they are involved comes from the good correlation between the degree of resistance and the carboxylesterase and paraoxon-degrading activity in aphid homogenates. Furthermore the carboxylesterase associated with resistance could not be separated from the insecticide-degrading enzyme by electrophoresis or ion-exchange chromatography. Homogenates of resistant aphids hydrolysed paraoxon 60 times faster than did those of susceptible aphids, yet the purified enzymes from both sources had identical catalytic-centre activities towards this substrate and also towards naphth-1-yl acetate, the latter being hydrolysed by both 2x10(6) times faster than paraoxon. These observations provide evidence that the enzyme from both sources is identical, and that one enzyme hydrolyses both substrates. This was confirmed by relating the rate of paraoxon hydrolysis to the rate at which paraoxon-inhibited carboxylesterase re-activated. Both had the same first-order rate constant (0.01min(-1)), showing clearly that the hydrolysis of both substrates is brought about by the same enzyme. Its K(m) for naphth-1-yl acetate was 0.131mm, and for paraoxon 75pm. The latter very small value could not be measured directly, but was calculated from substrate-competition studies coupled with measurements of re-activation of the diethyl phosphorylated enzyme. Since the purified enzymes from resistant and susceptible aphids had the same catalytic-centre activity, the 60-fold difference between strains must be caused by different amounts of the same enzyme resulting from mutations of the regulator gene(s) rather than of the structural gene.
对不同品系桃蚜的羧酸酯酶进行了检测，以试图了解它们对杀虫剂抗性的作用。它们参与其中的初步证据来自于抗性程度与蚜虫匀浆中羧酸酯酶及对氧磷降解活性之间的良好相关性。此外，与抗性相关的羧酸酯酶无法通过电泳或离子交换色谱与杀虫剂降解酶分离。抗性蚜虫的匀浆水解对氧磷的速度比敏感蚜虫的匀浆快60倍，但来自这两种来源的纯化酶对该底物以及对萘-1-基乙酸酯具有相同的催化中心活性，后者被这两种酶水解的速度均比对氧磷快2×10⁶倍。这些观察结果提供了证据，表明来自这两种来源的酶是相同的，并且一种酶能水解这两种底物。通过将对氧磷水解速率与对氧磷抑制的羧酸酯酶重新激活的速率相关联，这一点得到了证实。两者具有相同的一级速率常数（0.01min⁻¹），清楚地表明两种底物的水解是由同一种酶引起的。其对萘-1-基乙酸酯的K(m)为0.131mmol/L，对对氧磷为75pmol/L。后者这个非常小的值无法直接测量，而是通过底物竞争研究结合对二乙基磷酸化酶重新激活的测量来计算的。由于来自抗性和敏感蚜虫的纯化酶具有相同的催化中心活性，品系间60倍的差异必定是由调控基因而非结构基因突变导致相同酶的量不同所引起的。
