Denaturation studies on bovine pancreatic ribonuclease. Effect of trichloroacetic acid

Exposure of ribonuclease (EC 3.1.27.5) to 5% trichloroacetic acid solution is found to partially inactivate the enzyme. This inactivation is a function of time of exposure to trichloroacetic acid and reaches a plateau of about 45% residual activity. Higher concentrations of trichloroacetic acid lead to greater inactivation. Physicochemical properties such as sedimentation coefficient, gel-filtration behaviour and polyacrylamide gel electrophoresis of the trichloroacetic acid-treated enzyme remain unaffected as compared to the untreated enzyme. However, spectrophotometric titration of the trichloroacetic acid-treated enzyme revealed that one of the three 'buried' groups of tyrosine is exposed to the outside surface of the molecule. Near ultraviolet CD spectra supported these observations. Far ultraviolet CD spectra suggested some refolding of the enzyme after trichloroacetic acid treatment. Immunological determinants on the molecule remain unaltered upon trichloroacetic acid treatment. It is concluded that the exposed tyrosine group may be causing a conformational change in the protein and this change may be indirectly responsible for the observed reduction in the activity after trichloroacetic acid treatment.