Even though ample evidence exists suggesting a central function of PDI as a general oxidant of folding proteins, knowledge on particular substrates of PDI is largely missing. This is mainly due to the fact that previous studies to elucidate the PDI interactome have used trapping approaches that were designed to catch substrates for reduction. The present research proposal is therefore based on a novel trapping strategy expected to allow the identification and characterization of clients for PDI-mediated oxidation as well as of possible regulators of PDI oxidoreductase activity.