ABSTRACT
The kinetics of the electron transfer reaction between reduced [2Fe-2S] ferredoxins and select nitroimidazole antimicrobial agents is reported. The ferredoxins from the protozoan
Trichomonas vaginalis
and the cyanobacterium
Anabaena
sp. strain 7120 were studied because they are the proximal electron donors to nitroimidazoles in these two organisms with significantly different nitroimidazole susceptibilities. The rates of electron transfer from
Anabaena
ferredoxin to all nitroimidazoles were 1 to 2 orders of magnitude lower than for
T. vaginalis
ferredoxin. Quantitative structure-activity analysis of the kinetic data showed that the size of the alkyl substituent on the N-1 position of the imidazole ring strongly influenced the magnitude of the electron transfer rate constant. This implies that the distance between the iron-sulfur cluster and the nitro group of the imidazole is the critical variable in determining the rate of electron transfer. A correlation between the magnitude of the one-electron transfer rate constant with the susceptibility of the host organism to the cytotoxic effects of nitroimidazoles was also discovered. These results demonstrate that reductive activation is the most crucial step in determining the toxicity of nitroimidazoles.
摘要
报告了还原型[2Fe-2S]铁氧还蛋白与精选硝基咪唑类抗菌剂之间的电子转移反应动力学。来自原生动物
阴道毛滴虫
和蓝藻
Anabaena
菌株 7120 的铁氧还蛋白进行了研究,因为在这两种对硝基咪唑敏感性明显不同的生物体中,铁氧还蛋白是硝基咪唑的近端电子供体。电子从
Anabaena
铁毒素向所有硝基咪唑类化合物的电子传递速率都比
T. vaginalis
铁毒素的电子转移率低 1 至 2 个数量级。对动力学数据进行的定量结构-活性分析表明,咪唑环 N-1 位上烷基取代基的大小对电子转移速率常数的大小有很大影响。这意味着铁硫团簇与咪唑的硝基之间的距离是决定电子转移速率的关键变量。此外,还发现了单电子转移速率常数的大小与宿主生物对硝基咪唑的细胞毒性作用的敏感性之间的相关性。这些结果表明,还原活化是决定硝基咪唑毒性的最关键步骤。