Tryptophan repressor of Escherichia coli shows unusual thermal stability

Differential scanning calorimetry demonstrates that the tryptophan repressor of Escherichia coli is unusually resistant to thermal denaturation. The dimeric protein undergoes reversible dissociative unfolding at pH 7.5 centered at about 90 degrees C. The thermal stability may be due in part to the unusual structure of the protein, which is composed of two identical intertwined polypeptide chains.