Smith S T, Claycamp H G
Radiation Research Laboratory, University of Iowa Medical School, Iowa City 52242.
Int J Radiat Biol Relat Stud Phys Chem Med. 1988 May;53(5):829-37. doi: 10.1080/09553008814551161.
Survival of three strains of Escherichia coli K12 was studied with respect to radiation protection by dithiothreitol (DTT). The three strains compared were AB2462 recA, AB2470 rec21 and their DNA repair-competent prototype, AB1157. The strains were incubated in 10 mmol dm-3 DTT for 60 min and allowed an expression period for SOS functions to appear which may have been induced by DTT. Following the expression period the DTT-incubated cells and incubated control cells were irradiated. When AB1157 cells were pretreated with chloramphenicol (200 micrograms cm-3) for a period of 30 min prior to addition of the induction media no increase in survival was seen. When catalase (0.1 mg cm-3) was added to the AB1157 cells prior to the induction media a decrease in the degree of induction was noted with an enhancement ratio (ER) of 0.893 (ER-1 = 1.12). Furthermore, DTT-treated AB2462 and AB2470 demonstrated no increase in survival when compared to control cells. In radiation experiments on either strain of E. coli with or without DTT present during irradiation, the following were observed: (1) survival of AB1157 was enhanced with a dose modification factor (DMF) of 1.7 with DTT present and 1.3 with pretreatment; (2) the rec mutants showed no change in survival at any dose with a DMF of approximately 1.0. Results indicate that, using our protocol, inducible repair is of more importance than free radical scavenging by DTT. Furthermore, DTT-treated AB2462 demonstrated no increase in survival when compared to control cells. In radiation experiments on either strain of E. coli with and without DTT present during irradiation, the following were observed: (1) survival of AB1157 was enhanced with a DMF of 1.7 with DTT present during irradiation and 1.3 with only pretreatment; (2) the recA and recB mutants showed no change in cell survival at any dose with a DMF of approximately 1.0. Results indicate that, using our pretreatment protocol, inducible repair is of more importance in protection than free radical scavenging by DTT.
研究了三种大肠杆菌K12菌株在二硫苏糖醇（DTT）辐射防护方面的存活情况。所比较的三种菌株分别是AB2462 recA、AB2470 rec21及其具有DNA修复能力的原型菌株AB1157。将这些菌株在10 mmol dm-3的DTT中孵育60分钟，使可能由DTT诱导产生的SOS功能有一个表达期。在表达期之后，对经DTT孵育的细胞和孵育的对照细胞进行辐照。当在添加诱导培养基之前，将AB1157细胞用氯霉素（200微克 cm-3）预处理30分钟时，未观察到存活率增加。当在诱导培养基之前向AB1157细胞中加入过氧化氢酶（0.1毫克 cm-3）时，诱导程度降低，增强比（ER）为0.893（ER-1 = 1.12）。此外，与对照细胞相比，经DTT处理的AB2462和AB2470的存活率没有增加。在对大肠杆菌的任一菌株进行的辐射实验中，无论辐照期间是否存在DTT，观察到以下情况：（1）在存在DTT时，AB1157的存活率增强，剂量修正因子（DMF）为1.7，预处理时DMF为1.3；（2）rec突变体在任何剂量下存活率均无变化，DMF约为1.0。结果表明，按照我们的实验方案，诱导性修复比DTT清除自由基更为重要。此外，与对照细胞相比，经DTT处理的AB2462的存活率没有增加。在对大肠杆菌的任一菌株进行的辐射实验中，无论辐照期间是否存在DTT，观察到以下情况：（1）在辐照期间存在DTT时，AB1157的存活率增强，DMF为1.7，仅进行预处理时DMF为1.3；（2）recA和recB突变体在任何剂量下细胞存活率均无变化，DMF约为1.0。结果表明，按照我们的预处理方案，诱导性修复在防护中比DTT清除自由基更为重要。
