Thioredoxin Reductase from Rat Liver

The thioredoxin system was first identified in microorganisms where it participates in redox reactions, such as ribonucleotide reduction, transferring electrons from NADPH to the product formed. It contains two protein components, thioredoxin and thioredoxin reductase. A similar hydrogen transport system has now been demonstrated in rat liver. Using the liver thioredoxin previously isolated as a means of assaying thioredoxin reductase this enzyme has now been purified from the same source. A 100‐fold‐purification of thioredoxin reductase was obtained by treatment at pH 5 and chromatography on Sephadex and on DEAE‐cellulose. Thioredoxin reductase was found to be specific for NADPH. Ribonucleotide reductase, thioredoxin and thioredoxin reductase constitute a system necessary for the biosynthesis of deoxyribonucleotides. During liver regeneration, the level of ribonucleotide reductase was increased approximately 20‐fold. In contrast, the levels of thioredoxin and thioredoxin reductase remained constant.