Thioredoxins are small disulphide-containing redox proteins (within the conserved Cys-Gly-Pro-Cys active site) that have been found in all the kingdoms of living organisms. Thioredoxin contains a single disulfide active site and serves as a general protein disulphide oxidoreductase. Thioredoxins are involved in the first unique step in DNA synthesis. It interacts with a broad range of proteins by a redox mechanism based on reversible oxidation of two cysteine thiol groups to a disulphide, accompanied by the transfer of two electrons and two protons. The net result is the covalent interconversion of a disulphide and a dithiol. Trx also provides control over a number of transcription factors affecting cell proliferation and death throµgh a mechanism referred to as redox regulation. It has been sµggested that thioredoxin may catalyze the formation of correct disulfides during protein folding because of its ability to act as an efficient oxidoreductant. This could be especially useful in refolding proteins expressed in E. coli. To this end, thioredoxin has been shown to act as a protein disulfide isomerase.Its Molecular Weight is 11.9kDa. and the pI is 4.67.