Sulfiredoxin

In enzymology, a sulfiredoxin is an enzyme that catalyzes the chemical reaction


 * peroxiredoxin-(S-hydroxy-S-oxocysteine) + ATP + 2 R-SH $$\rightleftharpoons$$ peroxiredoxin-(S-hydroxycysteine) + ADP + phosphate + R-S-S-R

The 3 substrates of this enzyme are peroxiredoxin-(S-hydroxy-S-oxocysteine), ATP, and RSH, whereas its 4 products are peroxiredoxin-(S-hydroxycysteine), ADP, phosphate, and R-S-S-R.

This enzyme belongs to the family of oxidoreductases, specifically those acting on a sulfur group of donors with other, known, acceptors. The systematic name of this enzyme class is peroxiredoxin-(S-hydroxy-S-oxocysteine):thiol oxidoreductase [ATP-hydrolysing; peroxiredoxin-(S-hydroxycysteine)-forming]. Other names in common use include Srx1, sulphiredoxin, and peroxiredoxin-(S-hydroxy-S-oxocysteine) reductase.

Lower oxidation states of cysteine (disulfides) are readily reversible, higher oxidation states, such as sulfinic acid, were once considered irreversible, biologically speaking. This view changed with the discovery of sulfiredoxin, an enzyme that can reduce sulfinic acid back to thiol, in an ATP dependent manner. Additional work suggests that it plays a role in resolving mixed disulfides bonds. Initially discovered in yeast, sulfiredoxin is conserved in all eukaryotes, including mammals. In a perfect example of how multiple gene names can confuse the field, sulfiredoxin (Srxn1) was already known as a gene of unknown function, cloned by differential display of an in vitro model of tumorgenesis, and termed “Neoplastic progression 3/Npn3” although nothing about its actual function was reported. As a result, in most mouse microarray studies, sulfiredoxin is termed neoplastic progression 3, and typically classified as “cancer related” or “other” rather than as “antioxidant”. Npn3/Srxn1 is upregulated by an exceptionally large fold-magnitude in microarray studies of oxidative stress. Npn3/Srxn1 is induced up to 32-fold by D3T (liver), 12-fold by CdCl2, (liver), 4- to 10-fold by parcetamol (liver) and 3.3-flold by paraquat (heart). A survey of the GEO database also indicates a large induction of Npn3/Srxn1 is observed in injury to the lung by hyperoxia (data set GDS247, ID# 102780_at) or phosgene (GDS1244, 1451680_at). That Npn3 and Sxrn1 are synonyms of the same gene has not been pointed out in any of the 15 papers written on Srxn1 since its discovery. Because it was discovered so recently, the function of sulfiredoxin is not yet fully known and because no knockout of sulfiredoxin in mice is yet available, its true physiological importance remains to be established.