The Stereospecificity of Thioredoxin Reductase for Triphosphopyridine Nucleotide.

Escherichia coli B contains a cytidine diphosphate reductase system which utilizes reduced triphosphopyridine nucleotide to effect the reduction of cytidine diphosphate to deoxycytidine diphosphate (1, 2). Two components, thioredoxin and thioredoxin reductase, have been identified as oxidation-reduction carriers between TPNH and cytidine diphosphate. Thioredoxin is a low molecular weight protein which contains two sulfhydryl groups (1). Oxidized thioredoxin, containing a disulfide group (SZ), is reduced by the TPNH-specific thioredoxin reduct.ase according to the following equat.ion.