Abstract

Photodynamic inactivation is normally used to study or to modify the important amino acid residues involved in the active site of an enzyme. Horseradish peroxidase shows an exception with its resistance to dye-sensitized photooxidation with a normal low dye concentration. Using high concentration of eosin Y (20 folds), however, it was found possible to bind eosin Y on horseradish peroxidase by photodynamic action. After gel filtration on Sephadex G-150, two major fractions showing the binding of eosin Y on horseradish peroxidase with spectral changes were obtained. A significant shift of absorption peak from 517 nm to 523 nm for eosin Y binding was observed. One fraction shows a reduction of enzymatic activity, whereas, the other fraction exhibits no significant change of enzymatic activity.