Photoresponsive Cyclic Bis(cysteinyl)peptides as Catalysts of Oxidative Protein Folding This work was supported by the SFB 533 of the Ludwig-Maximilians Universität München (grant A8 Moroder/Oesterhelt).

The conformational transition of the disulfide-bridged bicyclic peptide (see picture) and of the related reduced monocyclic peptide induced by photoisomerization of the azobenzene moiety is responsible for significant differences in the redox properties. These can be exploited for photomodulation of rates and yields of in vitro oxidative folding of reduced and denatured RNase A as a model protein.