The rate-limiting step of sulfiredoxin is associated with the transfer of the γ-phosphate of ATP to the sulfinic acid of overoxidized typical 2-Cys peroxiredoxins

The eukaryotic sulfiredoxin (Srx) catalyzes the reduction of overoxidized typical 2-Cys peroxiredoxins PrxSO2 via ATP/Mg2+-dependent phosphorylation of the sulfinic acid group, followed by formation of a PrxSO-SSrx thiolsulfinate intermediate. Using real-time kinetics of wild-type and C84A Srxs, and pH-rate profiles with ATP/Mg2+ analogues, we show that the rate-limiting step of the reaction is associated with the chemical process of transfer of the γ-phosphate of ATP to the sulfinic acid, in contrast to that described by Jönsson et al. [7]. Two pKapps of 6.2 and 7.5 were extracted from the bell-shaped pH-rate profile, corresponding to the γ-phosphate of ATP, and to an acid–base catalyst, respectively.

Research highlights
► Sulfiredoxin is rate-limited by the process of transfer of the γ-phosphate of ATP.
► The rate of the process is governed by ionization of the γ-phosphate of ATP.
► Slow rate is not expected from the chemical reactivity of substrate sulfinic acid.