The effect of ultraviolet radiation and of soft X-rays on the sedimentation behaviour and light absorption of purified human serum albumin

Abstract

PROTEIN solutions are sensitive to ultraviolet light, and are coagulated by irradia- tion at the isoelectric point.' Coagulation can be prevented by irradiation either at reduced temperatures (0Q4) [Bovie, 1913] or in the presence of small amounts of acid or alkaJi (vide Arnow [1936] for references), but it then occurs if the tem- perature is raised, or the pH brought to the isoelectric point. It appears that coagulation of proteins by u.v. light takes place in at least two stages, a photo- chemical reaction independent of temperature, and an aggregation of the molecules attacked, a reaction of comparatively high temperature coefficient [Rajewsky, 1929; 1930; Clark, 1935]. The photochemical reaction causes in- creased light absorption Pedersen [1931], from preliminary experiments, reported that when serum albumin in solution at pH 3-5 was irradiated by u.v. light, the solution remained clear, the sedimentation constant doubled (indicating aggregation) and the diffusion constant showed a strong drift (indicating heterogeneity).