Component of the thioredoxin-thioredoxin reductase system which may be involved in biosynthesis of penicillins and cephalosporins and may be important in determining the thiol-disulfide redox balance. [thioredoxin]-dithiol + NADP(+) = [thioredoxin]-disulfide + H(+) + NADPH Binds 1 FAD per subunit. Homodimer. The active site is a redox-active disulfide bond. Belongs to the class-II pyridine nucleotide-disulfide oxidoreductase family.