Gardner P R, Fridovich I
Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710.
Arch Biochem Biophys. 1993 Feb 15;301(1):98-102. doi: 10.1006/abbi.1993.1120.
The effect of glutathione (GSH) on the superoxide-sensitive [4Fe-4S]-containing aconitase of Escherichia coli was explored. A mutant deficient in GSH biosynthesis, designated gshA, grew slower in a defined medium than did the parental strain and this effect was more pronounced when succinate was supplied as the carbon source in place of glucose. This suggested that the citric acid cycle was compromised in the gshA strain. Aconitase activity was approximately 25% lower in GSH-deficient cells growing on either glucose or succinate, and was lower still in strains producing less superoxide dismutase. Addition of GSH to the medium stimulated growth of the gshA strain on succinate. It also elevated the aconitase activity in the presence of chloramphenicol, which was added to block protein synthesis. Dithiothreitol and 2-mercaptoethanol were much less effective in this regard than was GSH. Exposure of cultures to 4.2 atm O2 caused a rapid decline in aconitase activity and this was the case in both GSH-proficient and GSH-deficient E. coli; however, the reactivation which was seen when the hyperoxic exposure was terminated was significantly impaired in the gshA strain. There is a dynamic balance between inactivation of aconitase by superoxide and reactivation by Fe(II) and this balance is altered in GSH-deficient E. coli. GSH may facilitate reactivation of aconitase, and of other [4Fe-4S]-containing dehydratases, by increasing the rate of transfer of Fe(II) to the [3Fe-4S] site.
研究了谷胱甘肽（GSH）对大肠杆菌中对超氧化物敏感的含[4Fe-4S]顺乌头酸酶的影响。一种缺乏GSH生物合成的突变体，命名为gshA，在限定培养基中的生长速度比亲本菌株慢，当以琥珀酸盐代替葡萄糖作为碳源时，这种影响更为明显。这表明gshA菌株中的柠檬酸循环受到损害。在以葡萄糖或琥珀酸盐为碳源生长的GSH缺陷型细胞中，顺乌头酸酶活性大约低25%，在超氧化物歧化酶产生较少的菌株中活性更低。向培养基中添加GSH可刺激gshA菌株在琥珀酸盐上的生长。在添加氯霉素以阻断蛋白质合成的情况下，它还提高了顺乌头酸酶的活性。在这方面，二硫苏糖醇和2-巯基乙醇的效果远不如GSH。将培养物暴露于4.2个大气压的氧气中会导致顺乌头酸酶活性迅速下降，GSH含量正常和GSH缺陷的大肠杆菌都是如此；然而，当高氧暴露终止时观察到的再激活在gshA菌株中显著受损。超氧化物使顺乌头酸酶失活与Fe（II）使其再激活之间存在动态平衡，而这种平衡在GSH缺陷的大肠杆菌中会发生改变。GSH可能通过提高Fe（II）向[3Fe-4S]位点的转移速率来促进顺乌头酸酶以及其他含[4Fe-4S]脱水酶的再激活。
