Determination of Free Radicals in Gamma Irradiated Proteins

Abstract

THE long-lived free radicals produced by gamma radiolysis of dry proteins at room temperature have been previously studied by electron spin resonance¹ (ESR). The carbon radicals which can be observed by ESR have been interpreted² as being predominantly located on glycine. Recently, the use of tritiated hydrogen sulphide as interceptor of free radicals has been proposed³ as a new experimental technique for determining the distribution of free radicals located on carbon atoms. The method in volves exposing the gamma irradiated lyophilized proteins to tritiated hydrogen sulphide in order to form carbon-tritium bonds in the protein. Tritium distribution among the amino-acids can be determined by subsequent hydrolysis, ammo-acid analysis and tritium counting; this measures the “secondary”1 free radical distribution. The terms “primary” and “secondary” free radicals refer, respectively, to (a) those radicals formed on irradiation at 77° K, and (b) those which arise from them on subsequent warming or which can be observed after radiolysis at room temperature.