Hammel K E, Cornwell K L, Buchanan B B
Proc Natl Acad Sci U S A. 1983 Jun;80(12):3681-5. doi: 10.1073/pnas.80.12.3681.
Thioredoxins are small redox proteins, alternating between the S-S (oxidized) and SH (reduced) states, that function in a number of important biochemical processes, including DNA synthesis, DNA replication, and enzyme regulation. Reduced ferredoxin is known to serve as the source of reducing power for the reduction of thioredoxins only in photosynthetic cells that evolve oxygen. In all other organisms, the source of hydrogen (electrons) for thioredoxin reduction is considered to be NADPH. We now report evidence that Clostridium pasteurianum, an anaerobic bacterium normally living in the soil unexposed to light, resembles photosynthetic cells in that it uses reduced ferredoxin as the reductant for thioredoxin. Moreover, the transfer of electrons from reduced ferredoxin to thioredoxin is catalyzed by a flavoprotein enzyme that has not been detected in other organisms. Our results reveal the existence of a pathway for the reduction of thioredoxin in which ferredoxin, reduced fermentatively either by molecular hydrogen or by a carbon substrate, provides the reducing power for the flavoprotein enzyme ferredoxin-thioredoxin reductase, which in turn reduces thioredoxin.
硫氧还蛋白是一种小型氧化还原蛋白，在S-S（氧化）态和SH（还原）态之间交替变化，参与许多重要的生化过程，包括DNA合成、DNA复制和酶调控。已知仅在能产生氧气的光合细胞中，还原型铁氧化还原蛋白是还原硫氧还蛋白的还原力来源。在所有其他生物体中，用于还原硫氧还蛋白的氢（电子）来源被认为是NADPH。我们现在报告证据表明，巴氏梭菌是一种通常生活在未暴露于光的土壤中的厌氧细菌，它类似于光合细胞，因为它使用还原型铁氧化还原蛋白作为硫氧还蛋白的还原剂。此外，从还原型铁氧化还原蛋白到硫氧还蛋白的电子转移由一种黄素蛋白酶催化，这种酶在其他生物体中尚未被检测到。我们的结果揭示了一种硫氧还蛋白还原途径的存在，其中铁氧化还原蛋白通过分子氢或碳底物发酵还原，为黄素蛋白酶铁氧化还原蛋白-硫氧还蛋白还原酶提供还原力，该酶进而还原硫氧还蛋白。
