PQQ, formally known as 2,7,9-tricarboxy-1H-pyrrolo [2,3-f] quinoline-4,5-dione, exists as an enzyme cofactor in bacterial methanol and glucose dehydrogenases. Since its discovery in 1979, the reactivity of PQQ has attracted much research attention. As PQQ is structurally similar to photochemically reactive phenanthrene-9,10-dione, illumination is expected to enhance its oxidation reactivity. We have confirmed this hypothesis; while D-Fructose is not a natural substrate of PQQ, when exposed to light, PQQ was found to oxidize this ketose. Our aim is to isolate and characterize the product of this light reaction. Further, our long-term goal is to study the scope of organic molecules oxidized by PQQ under illumination and to explore further applications of PQQ within soluble glucose dehydrogenase (sGDH) of bacterium Acinetobactor calcoaceticus as a biosensor.