Furlong C E, Li W F, Costa L G, Richter R J, Shih D M, Lusis A J
Department of Medicine, University of Washington, Seattle 98195-7360, USA.
Neurotoxicology. 1998 Aug-Oct;19(4-5):645-50.
Several organophosphorus insecticides and nerve agents are detoxified through the cytochrome P450/paraoxonase (PON1) pathway. PON1 is an HDL-associated enzyme encoded as a 355 amino acid protein in humans. The PON1 Arg192 isoform hydrolyzes paraoxon rapidly while the Gln192 isoform hydrolyzes this compound slowly. Both isoforms hydrolyze phenylacetate and chlorpyrifos oxon at approximately the same rate. We recently found that the effect of this polymorphism is dramatically reversed for sarin hydrolysis. The PON1 Arg192 isoform has virtually no sarinase activity while the Gln192 isoform has substantial activity. The Gln192 isoform also hydrolyzes diazoxon and soman faster than the Arg192 isoform. In addition to the large differences in rates of hydrolysis observed for some OP substrates by the two PON1 isoforms, there is also a large variability in serum PON1 concentrations that is stable over time between individuals. Thus, two factors govern the PON1 status of a given individual, the PON1 genotype as well as the amount of protein expressed from each allele. A two-dimensional enzyme analysis provides an excellent assessment of an individual's PON1 status, ie. the position 192 genotype as well as phenotype, or level of serum PON1 (Nature Genet 14:334-336). Do these interindividual differences in rates of substrate hydrolysis by PON1 reflect an individual's sensitivity or resistance to OP compounds processed through the P450/PON1 pathway? Injection of purified PON1 into mice clearly demonstrates the protective effect of having high serum levels of PON1 against toxicity by chlorpyrifos oxon or chlorpyrifos. Preliminary experiments with PON1 knockout mice, on the other hand, clearly demonstrate that low PON1 levels result in dramatically increased sensitivity to chlorpyrifos oxon. Attempts to express human PON1 in mice from constructs containing either of the human PON1 cDNA sequences were unsuccessful, despite the generation of the respective transgenic mice.
几种有机磷杀虫剂和神经毒剂可通过细胞色素P450/对氧磷酶（PON1）途径进行解毒。PON1是一种与高密度脂蛋白相关的酶，在人类中编码为一种含355个氨基酸的蛋白质。PON1 Arg192亚型能快速水解对氧磷，而Gln192亚型水解该化合物的速度较慢。两种亚型水解苯乙酸和毒死蜱氧磷的速度大致相同。我们最近发现，这种多态性对沙林水解的影响显著逆转。PON1 Arg192亚型几乎没有沙林酶活性，而Gln192亚型具有显著活性。Gln192亚型水解重氮磷和梭曼的速度也比Arg192亚型快。除了两种PON1亚型对某些有机磷底物的水解速度存在巨大差异外，个体血清PON1浓度也存在很大差异，且个体之间随时间保持稳定。因此，两个因素决定了个体的PON1状态，即PON1基因型以及每个等位基因表达的蛋白量。二维酶分析能很好地评估个体的PON1状态，即192位基因型以及表型，或血清PON1水平（《自然遗传学》14:334 - 336）。PON1对底物水解速度的这些个体间差异是否反映了个体对通过P450/PON1途径处理的有机磷化合物的敏感性或抗性？将纯化的PON1注射到小鼠体内清楚地表明，血清中高水平的PON1对毒死蜱氧磷或毒死蜱的毒性具有保护作用。另一方面，对PON1基因敲除小鼠进行的初步实验清楚地表明，低PON1水平会导致对毒死蜱氧磷的敏感性显著增加。尽管产生了相应的转基因小鼠，但尝试从包含任何一种人PON1 cDNA序列的构建体在小鼠中表达人PON1均未成功。
