Many proteins have been isolated from eukaryotes as redox-sensitive proteins, but whether these proteins are present in prokaryotes is not clear. Redox-sensitive proteins contain disulfide bonds, and their enzymatic activity is modulated by redox in vivo. In the present study, we used thiol affinity purification and mass spectrometry to isolate and identify 19 disulfide-bond-containing proteins in Pseudomonas putida exposed to potential oxidative damages. Among these proteins, we found that a typical 2-Cys Prx-like protein (designated PpPrx) displays diversity in structure and apparent molecular weight (MW) and can act as both a peroxidase and a molecular chaperone. We also identified a regulatory factor involved in this structural and functional switching. Exposure of pseudomonads to hydrogen peroxide (H(2)O(2)) caused the protein structures of PpPrx to convert from high MW complexes to low MW forms, triggering a chaperone-to-peroxidase functional switch. This structural switching was primarily guided by the thioredoxin system. Thus, the peroxidase efficiency of PpPrx is clearly associated with its ability to form distinct protein structures in response to stress.