Kinetic and structural assessment of the reduction of human 2-Cys peroxiredoxins by thioredoxins.

We have studied the reduction reactions of two cytosolic human peroxiredoxins (Prx) in their disulfide form by three thioredoxins (Trx; two human and one bacterial), with the aim of better understanding the rate and mechanism of those reactions, and their relevance in the context of the catalytic cycle of Prx. We have developed a new methodology based on stopped-flow and intrinsic fluorescence to study the bimolecular reactions, and found rate constants in the range of 10 -10  m  s in all cases, showing that there is no marked kinetic preference for the expected Trx partner. By combining experimental findings and molecular dynamics studies, we found that the reactivity of the nucleophilic cysteine (C ) in the Trx is greatly affected by the formation of the Prx-Trx complex.