Reduces disulfideprotein thioredoxin (Trx) to its dithiol-containing form. Homodimeric flavoprotein involved in the regulation of cellular redox reactions, growth and differentiation. Contains a selenocysteine residue at the C-terminal active site that is essential for catalysis. Also has reductase activity on hydrogen peroxide (H2O2). [thioredoxin]-dithiol + NADP(+) = [thioredoxin]-disulfide + H(+) + NADPH H(+) + H2O2 + NADPH = 2 H2O + NADP(+) Binds 1 FAD per subunit. Homodimer. ISGylated. The thioredoxin reductase active site is a redox-active disulfide bond. The selenocysteine residue is also essential for catalytic activity. Belongs to the class-I pyridine nucleotide-disulfide oxidoreductase family. Truncated C-terminus. Truncated C-terminus. Truncated C-terminus.