Molecular weights of blood plasma fractions photooxidized in the presence of sensitizers

Sensitized photooxidation of human blood plasma fractions, in contrast to high frequency electromagnetic irradiation of them, did not cause molecular splitting. On the contrary, an increase of the molecular weight was observed. This increase was, however, due only to the aggregation of a part of the molecules and its degree depend markedly on certain reaction conditions, such as temperature and protein concentration. By conducting the reaction at low temperature and low protein concentration and by reducing the reaction time, it was possible, at any rate when human serum albumin, γ-globulin and fibrinogen were used, to obtain photooxidized proteins of unchanged molecular weight. The fractions aggregated were separated by precipitation with ammonium sulphate. In order to maintain the molecular weight unchanged, sensitization by eosin seemed to be preferable to sensitization by methylene blue. The influence of photooxidation on sensitizer-protein interactions is discussed.