Reduced Flavin in Aqueous Solution Is Nonfluorescent

• DOI: 10.1021/acs.biochem.2c00538
• Publication Date: 2023-01-23T19:08:36Z
• Authors: Rylee A. McBride; David T. Barnard; Kimberly Jacoby-M...; Md. Harun-Or-Rashid; Robert J. Stanley
• Keywords: Flavin mononucleotide; Flavin adenine dinucleotide; Flavoprotein; Chromophore

Flavins are blue-light-absorbing chromophores with rich redox activity. Biologically, the most important riboflavin (vitamin B2), flavin mononucleotide, and adenine dinucleotide, latter two of which catalytic cofactors in enzymes. pivot between oxidized, one electron-, electron-reduced forms different protonation states, depending on enzymatic requirements. Some flavoenzymes use light as a reagent for chemical bond formation, photoinduced electron transfer, or conformational changes required light-sensitive signaling. Therefore, photochemistry photophysics flavins have received wide attention. Fluorescence from oxidized is often used to detect track oxidation states. However, there been conflicting reports over past 45 years whether reduced solution has detectable fluorescence. Here, using single photon counting emission spectroscopy rigorous sample preparation, we show definitively that essentially nonfluorescent, having quantum yield more than three orders magnitude lower flavin. This result will force re-evaluation experiments models assumed otherwise.