Photokinetic and Photophysical Measurements of the Sensitized Photooxidation of the Tryptophyl Residue in N‐acetyl Tryptophanamide and in Human Serum Albumin

Abstract

Abstract— The photosensitized oxidation of 10–100 μM N‐acetyl‐L‐tryptophanamide (NATA) in neutral aqueous solution and in the presence of various dyes proceeds by a pure O2(1Δg)‐involving mechanism. Incorporation of the tryptophyl (Trp) residue into the polypeptide chain of human serum albumin (HSA) has no influence on the mechanism and efficiency of Trp photooxidation when sensitized either by methylene blue, a non‐binding dye, or by rose bengal, a dye that gives non‐covalent 1: 1 complexes with HSA. This is due to the location of the Trp residue in close proximity of the protein surface and, in the case of rose bengal, to the coincidence of the photophysical properties (including the quantum yield of O2(1Δg) generation) for the free and HSA‐bound dye. Hematoporphyrin also binds to HSA with 1: 1 stoichiometry, although at a different site from rose bengal. Bound Hp again displays photophysical properties very similar with those of free Hp; however, the efficiency of Trp photo‐oxidation in HSA is about 5‐fold higher than in NATA owing to a limited rearrangement of the protein structure, induced by Hp binding, which enhances the probability of chemical quenching of O2(1Δg) by the indole ring.

Steady-state and time-resolved spectroscopic studies of photodynamic sensitizers: Porphyrins and phthalocyanines

“…Sinclair et al [32] reported a similarly long triplet lifetime for protoporphyrin (Pp) bound to the same protein. The yield of Hp triplet formation (0.66) in HSA is very similar to that found for free Hp in water at pH 7.4; the triplet is quenched by oxygen with a bimolecular constant of 1.7 x 108 M -1 s -1, i.e., one order of magnitude lower than that found for the uncomplexed dye [48]. This is probably due to the poorer ability of oxygen to diffuse into the protein matrix in the vicinity of the Hp binding site.…”

Critical Importance of the Triplet Lifetime of Photosensitizer in Photodynamic Therapy of Tumor

“…The quantum yield of the triplet state of the sensitizer, (biSc, does not differ significantly in most of porphyrins and metallo-porphyrins and is in the range from 1 to 0.3 (Reddi et al, 1987). Therefore, as is seen from Eqs.…”

“…In the cases of the porphyrins and metalloporphyrins used here, it is generally accepted that type I! mechanism dominates compared with type I mechanism (Kessel, 1984;Reddi et al, 1987). Therefore, we can put kRl 4 k,, [302].…”

The binding of analogs of porphyrins and chlorins with elongated side chains to albumin

“…The uptake of various sensitizers by albumin, and other serum proteins, has been studied extensively in the literature (Reddi et al 1987; Kongshaug 1992; Korbelik 1993; Gantchev et al 1999). In this study, we were interested in evaluating the effect of structural modifications of the sensitizers on the affinities of their binding to BSA and on the location of the bound sensitizers.…”