Fig. 8.

Thioredoxin/glutaredoxin system. a The oxidoreduction reaction between the thioredoxin (TXN) and its substrate (X protein). Reduced thioredoxin TXN-SH₂ binds to a target protein X via its hydrophobic surface area. Nucleophilic attack by the thiolate of Cys₃₂ results in the formation of a transient mixed disulfide, which is followed by a nucleophilic attack of the deprotonated Cys₃₅ generating oxidized TXN-S2 and the reduced protein, X-SH₂. b Deglutathionylation reaction by glutaredoxin (GLRX). c The oxidation of methionine generates a diastereomeric mixture of two stereoisomers methionine S-sulfoxide and methionine R-sulfoxide. Met-SO methionine sulfoxide MSRA and MSRB methionine sulfoxide reductase A and B, ROS reactive oxygen species. d Methionine sulfoxide reductase A reaction. MSRA methionine sulfoxide reductase A, TXN thioredoxin, GLRX glutaredoxin reductase, GSH glutathione