Abstract
Riboflavin (vitamin B2) is an important constituent of the prosthetic groups flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), which are utilized as electron-carriers in energy metabolism. Excitation by UV-light leads to the generation of riboflavin radicals and reactive oxygen species (ROS), which can oxidize a wide range of biomolecules. The human protein α1-microglobulin (A1M) is a reductase and a radical scavenger, which can protect cells and matrix against oxidative damage. Here, we provide evidence of a molecular interaction between illuminated riboflavin and A1M, similar to the radical scavenging reactions previously seen between A1M and other organic radicals. Binding between riboflavin and A1M was demonstrated by gel migration shift, UV-absorbance and fluorescence spectrum analysis. The reaction between A1M and UV-light illuminated riboflavin involved covalent modification of A1M and proteolytic release of an N-terminal part of the protein. Furthermore, A1M also inhibited the ROS-induced photoreduction reaction of riboflavin, in a reaction involving the free thiol group in position C34. Finally, the results show a protective effect of A1M, analyzed by gene expression rates of stress genes, against sublethal damage in retinal epithelial cells in culture. Together, our results suggest a new role of A1M as a scavenger of riboflavin radicals and ROS produced during illumination of riboflavin.
Highlights
Riboflavin (7,8-dimethyl-10-ribityl-isoalloxazine), which is generally referred to as vitamin B2, is a water-soluble vitamin that was discovered in 1872
No change in the absorbance spectra could be seen with A1M alone, when A1M was incubated with riboflavin in darkness, or when incubating ovalbumin (Figure 1B) or human serum albumin (HSA) with illuminated riboflavin under the same conditions
Riboflavin, or vitamin B2, is present in light-exposed parts of the human body (Cardoso et al, 2012), which render these tissues exposed to oxidative stress from riboflavin-derived radicals and reactive oxygen species (ROS) generated by illumination of the vitamin
Summary
Riboflavin (7,8-dimethyl-10-ribityl-isoalloxazine), which is generally referred to as vitamin B2, is a water-soluble vitamin that was discovered in 1872. Eggs, meat, and leafy vegetables have a high content of riboflavin, which makes them a main source of the vitamin. The most vital role of riboflavin is as a constituent of the prosthetic groups flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), which are important cofactors in energy metabolism. Riboflavin is mostly present as part of FAD and FMN, but it exists in its free form (Edwards, 2006)
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