Oxygen Effect as an Explanation of Differences between the Action of α-Particles and X- or γ-Rays on Aqueous Solutions of Amino-acids and Proteins

Abstract

Alexander and Rosen, working writh oxygen-free aqueous solutions of tryptophan and other substances, have discovered certain differences between the action of α-particles and of X-rays¹. They have also found such effects with proteins². In the case of aqueous solutions of benzene, the greater effectiveness of α-particles compared with X-rays in causing ring splitting (under oxygen-free conditions) is probably associated with the fact that the α-particles are producing relatively large amounts of oxygen simultaneously with free radicals, so that α-irradiation in the absence of added oxygen resembles X- or γ-irradiation in the presence of oxygen³. This explanation superseded a previous view that the α-particles were producing some more specific effect. The irradiation of tryptophan resembles that of benzene in that tryptophan undergoes ring splitting to formylkynurenine on X-irradiation in the presence of oxygen, but not in the absence of oxygen⁴, suggesting that an oxygen effect (or perhaps a hydrogen peroxide effect) might explain Alexander and Rosen's results. It would then be unnecessary to postulate the formation of activated hydrogen peroxide by α-particles. In order to obtain further evidence on this question, we have studied further the effect of oxygen on the γ-irradiation of aqueous tryptophan.