Purification and Properties of Rat‐Liver Thioredoxin

Rat liver thioredoxin, which could be reduced nonenzymatically by dithiothreitol, was identified by its ability to function as hydrogen donor in the conversion of ribonucleotides to deoxyribonucleotides catalyzed by ribonucleotide reductase both from the same tissue and from Escherichia coli. The latter enzyme was used to detect the reduced form of the thioredoxin during its purification which involved treatment at pH 5, chromatography on Sephadex G‐50, heat treatment, and DEAE‐cellulose chromatography. The isolated material was approximately 50% pure as determined by polyacrylamide electrophoresis. Liver thioredoxin is a heat‐stable protein of low molecular weight.