The comparative study of redox properties of recombinant human cytosolic and mitochondrial NADPH:thioredoxin reductases

We compared the redox properties of recombinant cytosolic (TrxR1) and mitochondrial (TrxR2) isoforms of human flavosulfoselenoenzyme NADPH:thioredoxin reductase. The standard redox potentials of isoenzymes (E-7(0)), determined according to the redox equilibrium with the NADP(+)/NADPH couple, were equal to -0.295 V (TrxR1) and -0.270 V (TrxR2). The more positive value of E-7(0) of TrxR2 may be attributed to the presence of His-125 at the vicinity of catalytic disulfide and selenylsulfide, instead of Tyr-116 in TrxR1. The reactivity of several quinones and nitroaromatic compounds towards TrxR1 and TrxR2 increased with their single-electron reduction potential (E-7(1)). For the first time, we studied the TrxR1-catalysed reduction of a series of aromatic N-oxides which were reduced in a mixed single- and two-electron way. Their reactivity was close to that of quinones and nitroaromatics with the similar values of E-7(1).