Comparison of cytochrome P450 from an insect and mammal,substrate specificity and the mechanism of selective inhibition

研究了一系列亚甲二氧苯（MDP）化合物对家蝇腹部和大鼠肝脏微粒体降解^<14> c -二嗪酮的抑制作用。几种MDP化合物选择性地抑制了昆虫的MFO活性，对哺乳动物的酶系统影响不大。当这些化合物与二嗪农、西威因和异氰菊酯联合局部施用于家蝇时，3,4-亚甲二氧苯-1-（2′-甲氧基乙氧基甲基醚）（简称1号）与所试任一杀虫剂均表现出良好的增效作用。1号对青桃蚜虫和小菜蛾幼虫也有增效作用。该化合物对拟除虫菊酯类抗性昆虫表现出较高的增效作用，恢复了杀虫剂的药效。另一方面，当该化合物与d-氨菊酯联合口服给鼠时，没有观察到协同作用。体外和体内实验结果表明，1号是一种具有良好选择性的MDP化合物。为了研究其选择性机制，我们检测了大鼠肝微粒体和几种MDP化合物获得的1型光谱。由于具有选择性的MDP化合物的Ks值明显小于不具有选择性的化合物，因此在昆虫和哺乳动物之间的选择性抑制可能涉及亲和力的差异。同样，与非选择性的MDP化合物相比，用大鼠肝微粒体获得的3型光谱也导致选择性的MDP化合物在lambda_<427>和lambda_<455>处的峰较小。由于从大鼠肝脏和家蝇腹部分离的同工酶数量不足，使用负责杀虫剂降解的特定细胞色素P450同工酶来检测mdp -细胞色素P450复合物形成的亲和力的尝试没有成功。

A series of methylenedioxyphenyl (MDP) compounds were evaluated for inhibition of degradation of ^<14>C-diazinon by microsomes from the housefly abdomen and rat liver. Several MDP compounds inhibited the insect MFO activity selectively with little effect on the mammalian enzyme system. When these compounds were applied topically to the housefly in combination with diazinon, carbaryl and resmethrin, 3,4-methylenedioxybenzene-1-(2'- methoxyethoxymethyl ether)(referred to as No.1) exhibited an excellent synergism with any of the insecticides tested. The synergism of No.1 was also confirmed against green peach aphids and diamondback moth larvae. The MDP compound showed especially high synergism against pyrethroid resistant strains of insect, restoring the efficacy of insecticide. On the other hand, no synergism was observed when the compound was administered orally to the rat in combination with d-resmethrin.The in vitro and in vivo results suggest the No.1 being a MDP compound with desiable selectivity.To investigate the mechanism of selectivity, the Type 1 spectra obtained with the rat liver microsomes and several MDP compounds were examined. Since the MDP compounds with selectivity showed significantly smaller Ks values than those without selectivity, a difference in the affinity appears to be involved in the selective inhibition between the insect and mammal. Similarly, the Type 3 spectra obtained with the rat liver microsomes also resulted in smaller peaks at lambda_<427> and lambda_<455> for the selective as compared with non-selective MDP compounds. An attempt to examine the affinity for MDP-cytochrome P450 complex formation using specific cytochrome P450 isozymes responsible for insecticide degradation was not successful due to insufficient amount of the isozymes isolated from the rat liver and housefly abdomen.