Electron-spin Resonance Studies of Bovine-serum Albumin and Cystine Irradiated with γ-rays at 77°K and at Room Temperature

Summary

Previous investigations at room temperature have shown that irradiated proteins, in general, give rise to only two types of resonance pattern. One of these is asymmetric and similar to that of cystine. This similarity has led to the postulate that unpaired electrons formed within the protein migrate to the sulphur atoms of the cystine residue.

We have found that the ESR spectrum obtained with BSA after irradiation in vacuum and examination at 77°k is different from that obtained on warming to room temperature. That observed on warming to room temperature is qualitatively the same as that obtained after irradiation in vacuum at room temperature, although the concentration of radicals in this latter case is greater.

With cystine the ESR pattern obtained after irradiation in a vacuum and examination at 77°k is different from that obtained on warming to room temperature. This radical observed on warming to room temperature is very stable and is also produced after irradiation in vacuum at room temperature. It is unaffected by oxygen.

While at room temperature the signals from cystine and BSA show some similarities, the spectra are quite different at 77°k, which reflects the primary radiation processes uncomplicated by secondary processes. Our work does not support the contention that the radicals produced have a high probability of migrating to the sulphur atoms.