Spectral-luminescent properties of chlorin e 6 and malate dehydrogenase complexes

Abstract

Spectral confirmation of the formation of stable equilibrium complexes (association constant K as = 2⋅10 6 M −1 ) of the Krebs cycle enzyme -malate dehydrogenase (MDH) -and one of the promising photodynamic sensitizers -chlorin e 6 -have been obtained. It is shown that the incorporation of dye molecules into the protein globule of dimeric MDH (each subunit of which contains 4 tryptophan amino acid residues, each binding one molecule of chlorin e 6 ) is accompanied by quenching of the tryptophan fluorescence of the enzyme. However, despite the overlapping of the fluorescence spectra of tryptophanyls of MDH and the absorption spectrum of chlorin e 6 , the fluorescence quenching observed is not caused by singlet-singlet inductive-resonant transfer of energy from the donor to the acceptor. The conclusion has been drawn that the reason for the absence of energy transfer from tryptophanyls to the dye is the more effective intertryptophan migration of energy to one of the most "longwave" amino acid residues, the quenching of the luminescence of which occurs due to the reversible photoinduced transfer of an electron to chlorin e 6 (formation of a complex with charge transfer). The formation of a complex with charge transfer between chlorin e 6 (when it is excited) and one of the amino acid residues of the enzyme that contact with the dye at its binding site on the protein molecule is also the most noncontradictory explanation of the observed (when bound with MDH) decrease in the quantum yield of fluorescence of chlorin e 6 upon increase in the duration of its quenching. The question of the ability of MDH to act as one of the most sensitive targets responsible for the disturbance of mitochondrial functions and initiation of the apoptosis of tumor cells in the process of photodynamic therapy is discussed.

Hitchhiking Nanoparticles: Mesenchymal Stem Cell-Mediated Delivery of Theranostic Nanoparticles

“…It suggests that Ce6 was interacting with biomolecules in FBS. 35 Free QDs in a serum-supplemented medium had a longer distribution of average FL lifetimes as well (⟨τ⟩ peak = 38.2 ns). Such changes in ⟨τ⟩ of free QDs can have various reasons.…”

“…Additionally, in a serum-supplemented medium, ⟨τ⟩ of Ce6 was longer (6 ns) (Figure D 2 ) compared to that of a serum-free medium (4.8 ns) (Figure D 1 ). It suggests that Ce6 was interacting with biomolecules in FBS . Free QDs in a serum-supplemented medium had a longer distribution of average FL lifetimes as well (⟨τ⟩ peak = 38.2 ns).…”

Biocompatible Supramolecular Systems Based on Chlorin e6: Preparation, Photophysical Properties

“…All measurements were conducted at 20 °С. The quantum yield of fluorescence of Ce 6 in complexes with excipients was calculated by the relative method using the formula j k = (j 0 A 0 I s k )/(A k I s 0 ), [25] where A and A 0 are the optical densities of solutions of Ce 6 complexed with excipients and of Ce 6 aqueous solution, respectively, at a wavelength of 410 nm; I and I 0 are the integrated fluorescence intensities (area under the fluorescence spectrum curve) of Ce 6 complexed Biocompatible Supramolecular Systems Based on Chlorin e 6 with excipients and in aqueous solution, respectively. The standard was the free form of Ce 6 in an aqueous solution, for which I 0 = 0.15 [26] ( Table 1).…”