Participates in various redox reactions through the reversible oxidation of its active center dithiol to a disulfide and catalyzes dithiol-disulfide exchange reactions (PubMed:16324156, PubMed:16387300). Shown to facilitate the reduction of insulin disulfide bonds (PubMed:16324156, PubMed:16387300). Might play a role in the reversible nitrosylation of cysteine residues in target proteins, and thereby contributing to the response to intracellular nitric oxide (PubMed:30014846). Shapes the ASJ sensory neuron biphasic response to nitric oxide (NO) exposure; trans-nitrosylation activity might inhibit calcium flux to the cytoplasm in ASJ neurons when exposed to a NO stimulus, whereas de-nitrosylation activity might promote calcium flux when NO is diminished (PubMed:30014846). By regulating the NO-induced ASJ sensory neuron activity, mediates the avoidance response to NO-producing organisms like P.aeruginosa (PubMed:30014846). Positively regulates life span extension under normal and caloric restriction conditions, dauer formation and the oxidative stress response (PubMed:16387300, PubMed:16324156, PubMed:21334311, PubMed:21304598, PubMed:26920757). Contributes to the down-regulation of expression of the insulin-like neuropeptide daf-28 in the ASJ neurons in a redox-independent fashion, thereby promoting dauer formation (PubMed:21304598). Negatively regulates the nuclear localization of the intestinal skn-1 transcription factor in a p38 MAPK pathway-dependent and redox-independent fashion (PubMed:26920757). Expressed in ASJ and ASI ciliated sensory neurons (PubMed:16387300, PubMed:21304598, PubMed:16324156, PubMed:21334311). Expressed in the intestine (at protein level) (PubMed:16324156). Expressed in larval stages L2 and L3 and increased expression during dauer stage (PubMed:21304598). Expressed in adult animals with increased expression in 10-day-old animals (PubMed:16324156). Up-regulated in response to dietary restriction and during dauer formation. Increased nitric oxide-evoked calcium flux to cytoplasm in ASJ sensory neurons (PubMed:30014846). Decreased avoidance of P.aeruginosa (PubMed:30014846). Decrease in lifespan (PubMed:16387300, PubMed:16324156). Suppression of lifespan extension induced by dietary deprivation or in an eat-2(ad1116) mutant background and partial suppression in a daf-2(e1370) mutant background (PubMed:21334311). Enhancement of the constitutive dauer formation phenotype in a daf-11(ks67), daf-11(m47), daf-11(sa195), daf-7(e1372), daf-1(e1287) or daf-8(e1393) mutant background at 15 degrees Celsius (PubMed:21304598). Suppression of the constitutive dauer formation phenotype in a daf-11(sa195), daf-28(tm2308) or daf-28(sa191) mutant background at 25 degrees Celsius (PubMed:21304598). Failure in down-regulation of daf-28 expression during dauer stage (PubMed:21304598). Decreased survival when facing oxidative stress upon exposure to sodium arsenite or paraquat (PubMed:26920757, PubMed:16324156). Increased localization of skn-1 to the nuclei of intestinal cells (PubMed:26920757). Suppression of skn-1 nuclear localization in a nsy-1(ok593), sek-1(km4) or pmk-1(km25) mutant background (PubMed:26920757). Belongs to the thioredoxin family.