Examination of Protein-Damaging Activity of Phosphorus(V) Porphyrin Photosensitizer for Photodynamic Therapy

Abstract

For the fundamental study of photodynamic therapy, protein-damaging activity of the water-soluble phosphorus(V) porphyrin (DDP(V)TPP) was examined. Absorption spectrum measurement demonstrated the binding interaction between DDP(V)TPP and human serum albumin, a water-soluble protein. Photo-irradiated DDP(V)TPP damaged the amino acid residue of human serum albumin, resulting in the decrease of fluorescence intensity from the tryptophan residue of human serum albumin. Protein damage photosensitized by DDP(V)TPP was inhibited by the addition of sodium azide and enhanced in deuterium oxide, indicating the contribution of singlet oxygen. However, sodium azide could not completely inhibit the damage of human serum albumin, suggesting that the electron transfer mechanism contributes to protein damage as does singlet oxygen generation. Isolated tryptophan was also damaged by a photosensitization of DDP(V)TPP in solution, whereas DDP(V)TPP did not induce photodamage to tyrosine and phenylalanine. Using the application of a fluorometry of hydrogen peroxide, the deactivation of catalase photosensitized by DDP(V)TPP was demonstrated.