Sulfiredoxin

In enzymology, a sulfiredoxin (EC 1.8.98.2) is an enzyme that catalyzes the chemical reaction

peroxiredoxin-(S-hydroxy-S-oxocysteine) + ATP + 2 R-SH

⇌

{\displaystyle \rightleftharpoons }

peroxiredoxin-(S-hydroxycysteine) + ADP + phosphate + R-S-S-R

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

This enzyme is involved in antioxidant metabolism by re-activating peroxiredoxins, which are a group of peroxidases, when these enzymes are inhibited by over-oxidation.

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.

Function

The sulfur atom in the side-chain of the amino acid cysteine can exist in several different oxidation states. The most reduced of these is as a thiol group (Cys-SH). Oxidation of cysteine produces cystine, which is one half of a disulfide bond (Cys-S-S-Cys). These lower oxidation states of cysteine (disulfides) are readily reversible, but higher oxidation states, such as sulfinic acid (Cys-SOOH), 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.