Phytofluene as a Highly Efficient UVA Photosensitizer of Singlet Oxygen Generation

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A. A. Ashikhmin^1,a, A. S. Benditkis^2,b, A. A. Moskalenko^1,c, and A. A. Krasnovsky, Jr.^2,d*

¹Institute of Basic Biological Problems, Federal Research Center “Pushchino Scientific Center for Biological Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia

²Bach Institute of Biochemistry, Federal Research Center of Biotechnology, Russian Academy of Sciences, 119071 Moscow, Russia

^* To whom correspondence should be addressed.

Received April 29, 2020; Revised May 26, 2020; Accepted June 4, 2020

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Phytoene and phytofluene – uncolored C₄₀ carotenoids with short chain of conjugated double bonds (3 and 5, respectively) – are known to be universal precursors in biosynthesis of colored carotenoids in photosynthesizing organisms. It is commonly recognized that C₄₀ carotenoids are photoprotectors of cells and tissues. We have shown that phytofluene is an exception to this rule. By measuring photosensitized phosphorescence of singlet oxygen (¹O₂) we found out that phytofluene was very effective photosensitizer of ¹O₂ formation in aerated solutions under UVA irradiation (quantum yield of 85 ± 5%), whereas phytoene was almost inactive in this process. It was demonstrated that both carotenoids quench singlet oxygen in the dark. The obtained quenching rate constants [(4 ± 1) × 10⁶ M^–1·s^–1 for phytoene and (2 ± 0.5) × 10⁷ M^–1·s^–1 for phytofluene] were smaller than the rate constant of the diffusion-controlled reactions by 3-4 orders of magnitude. Thus, both carotenoids displayed rather weak protector properties. Moreover, phytofluene due to its high photosensitizing activity might be considered as a promoter of cell photodamage and a promising UVA photosensitizer for medical purposes.

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KEY WORDS: phytofluene, phytoene, singlet oxygen, photosensitization, UVA

DOI: 10.1134/S0006297920070056

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