Stability of D-amino acid oxidase: denaturation by guanidine hydrochloride and urea

The guanidine hydrochloride-induced and urea-induced denaturations of swine D-amino acid oxidase (EC 1.4.3.3) dimer were studied by the measurements of the difference absorption spectra in the near-ultra violet region and specific activity. Spectral measurements were made at different pH values (8.3 and 3.2) and temperatures (27, 37 and 47 degrees C). It has been observed that (1), enzyme looses all its activity in concentrated solutions of the denaturants, and (2), the product of urea and guanidine hydrochloride denaturation is only partially unfolded as judged by the measurements of the intrinsic viscosity and exposures of the tyrosyl, tryptophyl and sulphhydryl residues.