Intermolecular and intramolecular reactions of human-serum albumin after its X-irradiation in aqueous solution

Abstract

The effect of 140 kv X-radiation on aqueous solutions of human-serum albumin has been studied by ultraviolet-absorption spectroscopy, supplemented by light-scattering measurements and ultracentrifuge examination. It is shown that, depending on the conditions of pH and ionic strength, the radiation can produce either or both of two effects: a partly reversible intermolecular effect of aggregation, and an irreversible intramolecular effect which can be detected spectroscopically. The intermolecular aggregation causes light-scattering, which affects the absorption coefficient in spectroscopic measurements. A method of correcting for this is used which, in isoelectric solutions where the radiation effect is almost entirely intermolecular, yields a value of the average molecular weight in quantitative agreement with direct light-scattering measurement. A two-stage process is proposed for the changes occurring in proteins in these conditions.