A synthetic model for the active site of the protein thioredoxin has been synthesized: corresponding to residues 31–35 of the protein and possessing the 14‒membered disulfide loop and a fluorescent chromophore. Dithiothreitol reduction of the disulfide bond results in a 50–60% enhancement of Trp fluorescence. The rate of reduction is solvent dependent, following the order 8 M urea » methanol > water. The spectral changes observed in the model peptide are compared with those reported for the native protein. Circular dichroism studies suggest a substantial change in peptide backbone conformation, on disulfide reduction.
