Electron Spin Resonance Studies of Radiation Damage to Amino Acids

The earlier investigation of radiation damage to certain amino acids with the method of electron spin resonance was extended to all the basic amino acids. Most amino acids when x-irradiated were found to have characteristic resonance patterns, each different from those found for the other amino acids. For most of them the characteristic patiern arises from hydrogen nuclear coupling with the electron spin. However. cysteine, cystine. and glutathione gave very similar resonance patterns. For these compounds the structure of the resonance appears to arise mainly from an anisotropy in the g-factor rather than from nuclear interactions. The common pattern of these sulfurcontaining amino acids suggests that the odd electron is mainly localized on the sulfur. The absence of resolvable structure for the resonances of x-irradiated tyrosine and tryptophan suggests that the odd electron giving the resonance may be migrating within the unsaturated rings of these substances. The evidence indicates that the tyrosine and tryptophan rings, in addition to sulfur groups, may in certain combinations act as protective agents to prevent radiation damage to other parts of the molecule. Tentative identifications of the free radicals produced by irradiation of a few of the acids are made from the structure of themore » resonances.« less