Protein disulfide oxidoreductases are ubiquitous redox enzymes that catalyse dithiol–disulfide exchange reactions with a CXXC sequence motif at their active site. Adisulfide oxidoreductase, a highly thermostable protein, was isolated from Pyrococcus furiosus(PfPDO), which is characterized by two redox sites (CXXC) and an unusual molecularmass. Its 3D structure at high resolution suggests that it may be related to the multidomain protein disulfide-isomerase (PDI), which is currently known only in eukaryotes
