Together with glutathione reductase gsr-1, required for the reduction of disulfide groups in the cuticle during molting. [thioredoxin]-dithiol + NADP(+) = [thioredoxin]-disulfide + H(+) + NADPH Binds 1 FAD per subunit. Homodimer. Expressed in intestine, pharynx, seam cells, hypodermis, rectal epithelial cells, neurons in the nerve ring and amphid sheath cells. Contains a selenide-sulfide bond between Cys-665 and Sec-666. This bond is speculated to serve as redox-active pair (By similarity). No obvious phenotype. RNAi-mediated knockdown of gsr-1 in mutants lacking trxr-1 causes an arrest during larval molting characterized by a partial detachment of the old cuticle and an impaired ability to reduce cuticle components. Also results in growth arrest during the postdauer molt. The active site is a redox-active disulfide bond. Belongs to the class-I pyridine nucleotide-disulfide oxidoreductase family.