Jürgen Baier, Tim Maisch, Max Maier, Eva Engel, Michael Landthaler, and Wolfgang Bäumler
(J. Baier, T. Maisch, M. Maier, E. Engl, M. Landthaler, and W. Bäumler)

Biophysical Journal, August 2006, Volume 91, Issue 4, Page 1452-1459
(Biophys. J. 2006 91: 1452-1459)

doi:10.1529/biophysj.106.082388

Abstract:
UVA light (320 - 400 nm) has been shown to produce deleterious biological effects in tissue due to the generation of singlet oxygen by substances like flavins or urocanic acid. Riboflavin, Flavin Mononucleotide (FMN), Flavin Adenine Dinucleotide (FAD), beta-Nicotinamide Adenine Dinucleotide (NAD), and beta-Nicotinamide Adenine Dinucleotide Phosphate (NADP), urocanic acid or cholesterol in solution were excited at 355 nm. Singlet oxygen was directly detected by time resolved measurement of its luminescence at 1270 nm. NAD, NADP and Cholesterol showed no luminescence signal possibly due to the very low absorption coefficient at 355 nm. Singlet oxygen luminescence of urocanic acid was clearly detected but the signal was too week to quantify a quantum yield. The quantum yield of singlet oxygen was precisely determined for Riboflavin (0.54 ± 0.07), FMN (0.51 ± 0.07) and FAD (0.07 ± 0.02). In aerated solution, Riboflavin and FMN generate more singlet oxygen than exogenous photosensitizers such as Photofrin, which are applied in photodynamic therapy to kill cancer cells. With decreasing oxygen concentration, the quantum yield of singlet oxygen generation decreased, which must be considered when assessing the role of singlet oxygen at low oxygen concentrations (inside tissue).

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