Redox activity distinguishes solid-state electron transport from solution-based electron transfer in a natural and artificial protein: cytochrome C and hemin-doped human serum albumin

The effect of the axial ligand fluorination of the water-soluble P(V)porphyrin complex on photosensitized protein damage was examined. The activity of singlet oxygen generation by diethoxyP(V) porphyrin was slightly improved by the fluorination of the ethoxy chains. Absorption spectrum measurements demonstrated the binding interaction between the P(V)porphyrins and human serum albumin, a water-soluble protein. Photo-irradiated P(V)porphyrins damaged the amino acid residue of human serum albumin, resulting in the decrease of the fluorescence intensity from the tryptophan residue of human serum albumin. A singlet oxygen quencher, 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. The decrease of the fluorescence lifetime of P(V)porphyrin by human serum albumin supported the electron transfer mechanism. The estimated contributions of the electron transfer mechanism are 0.57 and 0.44 for the fluorinated and non-fluorinated P(V)porphyrins, respectively. The total quantum yield of the protein photo-oxidation was slightly enhanced by this axial fluorination.

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Tetrakis(N-methyl-p-pyridinio)porphyrin and its zinc complex can photosensitize damage of human serum albumin through electron transfer and singlet oxygen generation

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424616500991 ◽

2016 ◽

Vol 20 (07) ◽

pp. 813-821 ◽

Cited By ~ 11

Author(s):

Dongyan Ouyang ◽

Shiori Inoue ◽

Shigetoshi Okazaki ◽

Kazutaka Hirakawa

Keyword(s):

Electron Transfer ◽

Human Serum Albumin ◽

Serum Albumin ◽

Singlet Oxygen ◽

Human Serum ◽

Sodium Azide ◽

Zinc Complex ◽

Transfer Mechanism ◽

Protein Damage ◽

Electron Transfer Mechanism

The photosensitized protein-damaging activity of water-soluble freebase tetrakis([Formula: see text]-methyl-[Formula: see text]-pyridinio)porphyrin (H2TMPyP), and its zinc complex (ZnTMPyP) was investigated using human serum albumin (HSA) as a target protein. These porphyrins bound to HSA and caused photosensitized oxidation of the tryptophan residue. The protein damage was enhanced in deuterium oxide and inhibited by sodium azide, a physical quencher of singlet oxygen, suggesting the contribution of singlet oxygen. However, an excess amount of sodium azide could not completely inhibit protein damage. These findings suggest the partial contribution of another mechanism to the protein damage, possibly the electron transfer mechanism. The Gibbs free energy of the electron transfer mechanism showed that electron transfer-mediated tryptophan oxidation by photoexcited H2TMPyP is more advantageous than that by ZnTMPyP. Actually, the quantum yield of protein damage through electron transfer by H2TMPyP was larger than that by ZnTMPyP. In addition, this study demonstrated that the association between porphyrin and protein plays an important role in photosensitized protein damage.

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