Inactivation of Ribonuclease by the Primary Aqueous Radicals

The separate contributions of the primary aqueous radicals to the changes in activity, molecular configuration and amino acid composition of RNase, produced by γ-irradiation of dilute solutions, have been identified. The most effective radical for the inactivation of RNase is the H atom; approximately one out of four H atoms inactivates a RNase molecule, compared to 1 out of 15 ·OH or e_ eq⁻ . Additional molecular products are formed on irradiation of the enzyme and when separated by gel filtration these have been related to denatured and aggregated forms of the protein molecule. Hydroxyl radicals are most effective in forming molecular aggregates while H atom attack leads predominantly to denaturation. The solvated electron is the least effective radical for producing changes in molecular configuration; both denatured and aggregated products are formed. In the presence of oxygen, the denatured product forms few, if any, aggregates, due presumably to peroxy formation ...