Gaudu P, Fontecave M
Laboratoire d'Etudes Dynamiques et Structurales de la Sélectivité, Université Joseph Fourier, Grenoble, France.
Eur J Biochem. 1994 Dec 1;226(2):459-63. doi: 10.1111/j.1432-1033.1994.tb20070.x.
The NADPH:sulfite reductase of Escherichia coli is a soluble enzyme that has a subunit structure alpha 8 beta 4, where the alpha subunit is a flavoprotein and the beta subunit is a metalloprotein. Overexpression of the holoenzyme in E. coli has greatly simplified the purification of this enzyme. Under aerobic conditions, recombinant sulfite reductase catalyzes the reduction of 1,1'-dimethyl-4,4'-bipyridinium dichloride (paraquat) by NADPH, with Km values for paraquat and NADPH of approximately 70 microM and 80 microM, respectively. Since pure flavoprotein alpha subunit, encoded by the cysJ gene, has similar catalytic activities, it is suggested that paraquat receives electrons directly from the alpha subunit. A mutant strain lacking an active cysJ gene is resistant to paraquat. The NADPH:ferredoxin reductase of E. coli is also a paraquat reductase but with much higher Km values for paraquat and lower enzyme activities. These results suggest that the sulfite reductase is a major paraquat reductase in E. coli and is responsible for the toxic activation of the drug.
大肠杆菌的NADPH：亚硫酸盐还原酶是一种可溶性酶，具有α8β4亚基结构，其中α亚基是黄素蛋白，β亚基是金属蛋白。该全酶在大肠杆菌中的过表达极大地简化了这种酶的纯化过程。在有氧条件下，重组亚硫酸盐还原酶催化NADPH还原1,1'-二甲基-4,4'-联吡啶二氯化物（百草枯），百草枯和NADPH的Km值分别约为70μM和80μM。由于由cysJ基因编码的纯黄素蛋白α亚基具有相似的催化活性，因此表明百草枯直接从α亚基接收电子。缺乏活性cysJ基因的突变菌株对百草枯具有抗性。大肠杆菌的NADPH：铁氧化还原蛋白还原酶也是一种百草枯还原酶，但对百草枯的Km值高得多，酶活性较低。这些结果表明，亚硫酸盐还原酶是大肠杆菌中主要的百草枯还原酶，并负责该药物的毒性活化。
