The activities of the two thioredoxins from Streptomyces aureofaciens are not interchangeable.

The physico-chemical features of the NADPH-thioredoxin reductase (TRR) and two thioredoxins from Streptomyces aureofaciens (A14) are reported. The activity of pure S. aureofaciens thioredoxin reductase decreased drastically in the presence of NADPH or NADH while NADP(+), NAD(+), as well as S. aureofaciens thioredoxin-1 (TR1) activated the enzyme activity significantly. TR1 fully protected the enzyme from inactivation and also promoted its complete reactivation. S. aureofaciens thioredoxin-2 (TR2) did not protect thioredoxin reductase from NADPH inactivation. The results indicate that although the two thioredoxins from S. aureofaciens have similar biochemical properties, their essential oxidoreductase activities are not interchangeable.