Electron Spin Resonance Studies on the Damage of Ribonuclease Exposed to Ultra-violet Light

Abstract

Primary damage in RNase caused by exposure to UV-light was studied by ESR. Frozen aqueous solution of RNase was irradiated by 254 mμ light and ESR spectra and remaining enzymatic activity were measured. ESR spectra showed that the free radicals formed in RNase were localized in chromophores of RNase ; namely tyrosine, phenylalanine and cystine. Effect of warming on the spectra suppored the assignments. The amount of radicals in RNase had linear relationship with the extent of enzyme inactivation.