Photoinduced conformational changes of human serum albumin bound to protoporphyrin IX and hemin

Abstract

Irradiation of porphyrins bound to proteins applies to photodynamic cancer therapy, photo-reduction of water, and the possibility of modifying proteins to impart new functions. Upon binding Protoporphyrin IX (PPIX) and hemin, respectively, to human albumin (HSA), the bound products' response to low-dose irradiation at pH 7.4 is examined in this study. Spectroscopic data suggests that irradiation of PPIX when bound to HSA causes small secondary and tertiary protein conformational changes. Alternately, sizeable alterations are not seen when hemin bound to HSA is irradiated. This difference indicates a different photophysical mechanism for PPIX than for hemin.