The thioredoxin system consists of thioredoxin, thioredoxin-reductase and NADPH. Thioredoxin from E. coli consists of a single polypeptide chain of 108 amino acids with a molecular weight of 11,700. The protein contains no prosthetic group or bound metals.
Thioredoxin is a small electron transport protein that serves as the hydrogen donor in the enzymatic reduction of ribonucleotides to deoxyribonucleotides. The thioredoxin system is involved in other reductive processes such as the enzymatic reduction of methionine sulfoxide and sulfate. The oxidation-reduction function of thioredoxin is linked to a single intra-molecular disulfide bridge, forming a 14 member ring. The system is particularly useful for high level production of soluble fusion proteins in the E. coli cytoplasm. In many cases, these fusion proteins fold correctly and thus display full biological activity.
