21] Thioredoxin and thioredoxin reductase

Abstract

Publisher Summary This chapter summarizes current methods to determine Trx and thioredoxin reductase (TR). Thioredoxin (Trx) is a small (Mr 12,000) multifunctional and ubiquitous protein characterized by having a redox-active disulfide/dithiol within the conserved active site sequence: -Trp-Cys-Gly-Pro-Cys-. Oxidized thioredoxin (Trx-S 2 ) has a disulfide, and reduced thioredoxin [Trx-(SH) 2 ] has a dithiol. Thioredoxin reductase specifically reduces Trx-S 2 to Trx-(SH) 2 using NADPH. The Trx-(SH) 2 form is a powerful protein disulfide reductase. Thus, Trx, TR, and NADPH, collectively called the thioredoxin system, operate as a powerful NADPH-dependent protein disulfide reductase system. Thioredoxin has been isolated and characterized from a wide variety of prokaryotic and eukaryotic species. Mammalian thioredoxins show about 25% sequence identity to the well-characterized E. coli protein with 108 residues. One classic function of the thioredoxin system is to act as a hydrogen donor for ribonucleotide reductase, which is essential for DNA synthesis. Redox control processes involve changes in the activity of an enzyme, a receptor, or a transcription factor via dithiol/disulfide interchange reactions. Mammalian thioredoxin reductase, with its broader substrate specificity, is likely to be involved in multiple signaling systems for redox control of cellular processes.