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本文报告了三尖杉酯碱抑制艾氏腹水癌细胞DNA聚合酶α的动力学。三尖杉酯碱的抑制作用与反应体系中的模板DNA量有关,过量的DNA可降低药物的抑制作用,但不能完全消除药物的抑制。并证明三尖杉酯碱与模板DNA对DNA聚合酶α是混合型抑制,当三尖杉酯碱浓度为10μM时,其K_i值为9.5μM,K_m值为13μg DNA/100μl。三尖杉酯碱抑制DNA聚合酶α的能力不受反应体系中四种脱氧核苷三磷酸底物浓度的影响,通过同时改变四种底物浓度,或固定三种底物浓度只改变其中一种底物的量,或采用限制性DNA合成系统(Limited DNA Synthesis)即在完全体系中省略去某一底物,均证明三尖杉酯碱与四种底物对DNA聚合酶α为非竞争性抑制,当三尖杉酯碱浓度为4μM时,对dCTP、dGTP和dTTP的K_i值分别为12μM、11μM和12μM。本文也比较了三尖杉酯碱衍生物——高三尖杉酯碱、异三尖杉酯碱和表三尖杉酯碱对DNA聚合酶α的抑制作用。结果表明,当药物浓度相同时,高三尖杉酯碱的作用较三尖杉酯碱和异三尖杉酯碱强,而三尖杉酯碱和异三尖杉酯碱的作用相近;表三尖杉酯碱本身对DNA聚合酶α无抑制作用,也未见其在无细胞系统中对三尖杉酯碱的抑制能力有加强作用。以上药物对E.coli DNA聚合酶Ⅰ也有相似的抑制作用。
This paper reports the kinetics of harringtonine in inhibiting DNA polymerase alpha in Ehrlich ascites carcinoma cells. The inhibitory effect of harringtonine is related to the amount of template DNA in the reaction system. Excess DNA can reduce the inhibitory effect of the drug, but cannot completely eliminate the inhibition of the drug. It was also proved that harringtonine and the template DNA were mixed inhibited by DNA polymerase α. When the harringtonine concentration was 10 μM, the K_i value was 9.5 μM, and the K_m value was 13 μg DNA/100 μl. The ability of harringtonine to inhibit DNA polymerase alpha is not affected by the concentration of the four deoxynucleoside triphosphate substrates in the reaction system, by changing the concentration of four substrates simultaneously, or fixing only one of the three substrate concentrations to change only one of them. The amount of substrate, or the use of a restricted DNA synthesis system that omits a substrate in the complete system, demonstrates that the harringtonine base and the four substrates are not competitive with DNA polymerase alpha. Suppression, when the harringtonine base concentration was 4 μM, the K i values for dCTP, dGTP, and dTTP were 12 μM, 11 μM, and 12 μM, respectively. In this paper, the inhibitory effects of homoharringtonine derivatives, homoharringtonine, isoharringtonine, and epidaunionine on DNA polymerase α were also compared. The results showed that when the drug concentration was the same, homoharringtonine was more potent than harringtonine and isoaharringtonine, while harringtonine and isoaharringtonine were similar; The ferucilline base itself has no inhibitory effect on the DNA polymerase alpha, nor does it have a potentiating effect on the inhibitory ability of the harringtonine in a cell-free system. The above drugs also have similar inhibitory effects on E.coli DNA polymerase I.