Hassan H M, Fridovich I
J Biol Chem. 1979 Nov 10;254(21):10846-52.
Paraquat mediates a superoxide dismutase-inhibitable reduction of cytochrome c by suspensions of Escherichia coli B. Glucose was most effective in providing electrons for this cytochrome c reduction, but other nutrients could serve in this capacity, provided the cells were preconditioned by growth on these nutrients. Paraquat reduction depended upon a NADPH:paraquat diaphorase, present in the cytosol. Reduced paraquat could diffuse across the cell envelope and react with dioxygen, in the suspending medium, thus generating O2- in that compartment. Most of the paraquat reduced in the cell, under the conditions used, reoxidized in situ and most of the O2- production was thus intracellular. The partitioning of reduced paraquat between intracellular and extracellular compartments, prior to reaction with dioxygen, depended upon intracellular pO2 and any strategy which raised intracellular pO2 decreased the efflux of reduced paraquat and thus decreased extracellular O2- production. Extracellular O2- and H2O2 did contribute to cell damage in proportion to the amount produced. O2- appeared to be unable to cross the cell envelope in either direction and the only O2- which was effective in raising the rate of biosynthesis of the manganese-superoxide dismutase, was that generated within the cell.
百草枯可介导大肠杆菌B菌悬液对细胞色素c进行超氧化物歧化酶可抑制的还原反应。葡萄糖在为该细胞色素c还原反应提供电子方面最为有效，但其他营养物质也可发挥此作用，前提是细胞预先在这些营养物质上生长进行预处理。百草枯的还原依赖于存在于胞质溶胶中的NADPH：百草枯双加氧酶。还原态的百草枯可扩散穿过细胞膜，与悬浮介质中的双氧反应，从而在该隔室中产生超氧阴离子。在所使用的条件下，细胞内还原的大部分百草枯会原位再氧化，因此大部分超氧阴离子的产生是在细胞内。在与双氧反应之前，还原态百草枯在细胞内和细胞外隔室之间的分配取决于细胞内的氧分压，任何提高细胞内氧分压的策略都会减少还原态百草枯的外流，从而减少细胞外超氧阴离子的产生。细胞外的超氧阴离子和过氧化氢确实会按产生量的比例对细胞造成损伤。超氧阴离子似乎无法双向穿过细胞膜，而唯一能有效提高锰超氧化物歧化酶生物合成速率的超氧阴离子是细胞内产生的。
