Determination of Singlet Oxygen and Electron Transfer Mediated Mechanisms of Photosensitized Protein Damage by Phosphorus(V)porphyrins

The mechanism of photosensitized protein damage by phosphorus(V) tetraphenylporphyrin derivatives (P(V)TPPs) was quantitatively clarified. P(V)TPPs bound to human serum albumin (HSA), a water-soluble protein, and damaged its tryptophan residue during photoirradiation. P(V)TPPs photosensitized singlet oxygen (1O2) generation, and the contribution of 1O2 to HSA damage was confirmed by the inhibitory effect of sodium azide, a 1O2 quencher. However, sodium azide could not completely inhibit HSA damage, suggesting the contribution of an electron transfer mechanism to HSA damage. The decrement in the fluorescence lifetime of P(V)TPPs by HSA supported the electron transfer mechanism. The contribution of these processes could be determined by the kinetic analysis of the effect of sodium azide on the photosensitized protein damage by P(V)TPPs.