Inactivation of Ribonuclease A in Aqueous Solution by Ionizing Radiation

Ribonuclease A were gamma-irradiated in a dilute aqueous solution. The G° value of inactivation of the enzyme was 0.45. When the enzyme lost its enzymatic activity significantly, some physicochemical or chemical properties were found to be altered, while others were not. Unaltered properties were ‘type’ of amino acid terminals, optimum pH and pH-enzyme activity curves. Properties affected by irradiation were a destruction of some amino acid residues, an alteration of electrophoretic mobility, and an incresed reactivity to diazo-1-H-tetrazole. The extents of alteration of the latter two properties were dependent upon the radiation dose. These results suggest that the ionizing radiations induce a local conformational change in the enzyme molecule and that this may play an important role in the inactivation of the enzymatic activity of ribonuclease A.