Temperature dependence of the radiation inactivation of proteins

The radiation inactivation method allows determination of the relative molecular mass (Mr) of proteins by exposure to high doses of ionizing radiation. The analysis by target theory of biological activity decay curves yields the size of the protein. A correction factor for Mr has been routinely used in the literature when irradiation is conducted at low temperature. Since the radiation inactivation of proteins is affected by temperature, we propose a general equation which relates Mr of a protein to D37,t, the dose in megarads at a given temperature t (in degree C) where 37% of its initial biological activity remains log Mr = 5.89 - log D37,t - 0.0028t. It is concluded that temperature affects the amount of absorbed radiation energy required to inactivate 1 mol of protein.