Inactivation and Induction of Free Radicals in Dried Trypsin

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Abstract
An investigation has been carried out of inactivation and induction of stable free radicals in crystalline trypsin exposed to UV-light at about 10[degree]C or irradiated with Co60 gamma-rays at about 0[degree]C. It was found that the ESR-signal induced by gamma-rays resembled closely that induced by UV-light. The number of observed gamma-ray-induced radicals reached a constant value of about 0.6 radicals/ molecule when the inactivation exceeded 50%. By extrapolation to zero dose it was calculated that in the case of gamma-rays 4 radicals, of which less than one is of the sulfur type, are induced per molecule inactivated. For trypsin subjected to UV-light it was found that the concentration of radicals increased almost linearly with the degree of inactivation. In this case less than 0.2 radical, of which about 0.06 is of the sulfur type, is induced per molecule inactivated. The relationships between the number of radicals induced and the corresponding inactivation can for both radiations be described mathematically in the same way, namely on the assumption that in a homogeneously irradiated material the rate of increase of inactivated molecules as well as that of induced radicals depend exponentially on the dose. Thus, the principal differences between the results obtained with the two radiations are (1) that the radical saturation value in the case of UV-radiation is only about 1/3 of that for gamma-rays, and (2) that the number of radicals associated with each inactivated molecule is about 25 times higher in the case of gamma-rays than in the case of UV-light. The results indicate that the observed inactivation of dry trypsin at least in part is independent of the ac -companying long lived free radicals.