Formation of >C=O Bonds in the Radiation-induced Oxidation of Protein in Aqueous Systems

Abstract

A SERIES of observations recently made indicate that formation of the >C=O bond is a principal chemical effect of the attack of hydroxyl radicals on protein in oxygenated solution. Irradiations were made in a neutron flux produced by bombardment of beryllium with 24-MeV. deuterons in the Crocker Laboratory 60-in. cyclotron. Solutions were exposed under one atmosphere of oxygen in sealed ‘Pyrex’ cells mounted in a motor-driven reel situated 15 cm. from the beryllium target. One of the cells in each exposure contained a formic acid–oxygen dosimeter¹. (We employed the formic acid–oxygen dosimeter to obtain an estimate of the relative number of water molecules decomposed via (1) H₂O = H + OH and (2) H₂O = ½H₂ + ½H₂O₂. Absolute yield values could then be calculated in terms of G(molecules/100 eV.), since in dilute solutions at pH values above 2.5, the sum G(1) + G(2) = G(H₂O) is to a first approximation independent of the quality of the absorbed radiation¹. With our standard geometry for neutron exposures, we obtained G(1) = 2.68, G(2) = 0.97 on the basis of G(H₂O) = 3.65².)