Relative contributions of thioltransferase-and thioredoxin-dependent systems in reduction of low-molecular-mass and protein disulphides

Abstract

Two enzyme systems capable of reducing disulfide bonds both in low-MW compounds and in polypeptides and proteins exist. One consists of thioltransferase in combination with reduced glutathione and glutathione reductase, and the second consists of thioredoxin in combination with thioredoxin reductase. The relative effectiveness in catalyzing disulfide reduction of various substrates in rat liver cytosol was evaluated in the present study. The thioltransferase-dependent system was more efficient in reducing small molecules. Insulin was most effectively reduced by the thioredoxin system. Bovine trypsin was a better substrate for thioltransferase, and partially proteolyzed bovine serum albumin was equally good for the 2 systems. Thus, in the case of protein disulfide bonds, the nature of the particular substrate used determines which of the 2 reducing systems is the more important.