FIG. 7.

Proposed reaction mechanism for regulation of PCD by Trx3. Reduction of H₂O₂ by Prx1 results in oxidation of the peroxidatic Cys residue (Cys91) of Prx1 to the sulfenic acid form (Prx1-SOH). Reaction with GSH generates glutathionylated Prx1 (Prx1-S-SG) (1), which is a substrate for reduction by Trr2 in a reaction that requires GSH to regenerate reduced Prx1. Alternatively, Prx1-SOH reacts with the catalytic Cys residue (Cys55) of Trx3 to form a disulfide-bonded intermediate (2). This intermediate can be reduced by the second Cys residue in Trx3 (Cys58) generating oxidized Trx3 and reduced Prx1. Oxidized Trx3 can be reduced by Trr2 to prevent activation of PCD. PCD, programmed cell death.