Electron Spin Resonance Studies of Radiation Damage to Proteins

Abstract

Electron spin resonance of free radicals produced by X-irradiation of various types of proteins has been observed. Generally, only 2 types of resonance pattern were observed, either separately or in combination. One of these patterns is field-dependent and characteristic of cystine or cysteine, and the other is a doublet similar to that of irradiated polyglycine. Effects of orientation of the sample in the applied magnetic field were observed for silk and feather quill. The total spread of the cysteine-like resonance depends on the strength of the applied magnetic field or the frequency at which the resonance is observed. Effects of absorbed O2 were noted for several samples. The double resonance is converted by O2 to a relatively sharp but field-dependent resonance believed to arise from a peroxide radical, ROO, formed by combination of molecular oxygen with radicals originally produced by the X-irradiation. The cystinelike resonance is killed by O2 without the production of an observable secondary radical.