A Bifunctional Molecule as an Artificial Flavin Mononucleotide Cyclase and a Chemosensor for Selective Fluorescent Detection of Flavins

Abstract

Flavins, comprising flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), and riboflavin (RF, vitamin B(2)), play important roles in numerous redox reactions such as those taking place in the electron-transfer chains of mitochondria in all eukaryotes and of plastids in plants. A selective chemosensor for flavins would be useful not only in the investigation of metabolic processes but also in the diagnosis of diseases related to flavins; such a sensor is presently unavailable. Herein, we report the first bifunctional chemosensor (PTZ-DPA) for flavins. PTZ-DPA consists of bis(Zn(2+)-dipicolylamine) and phenothiazine. Bis(Zn(2+)-dipicolylamine) (referred to here as XyDPA) was found to be an excellent catalyst in the conversion of FAD into cyclic FMN (riboflavin 4',5'-cyclic phosphate, cFMN) under physiological conditions, even at pH 7.4 and 27 degrees C, with less than 1 mol % of substrate. Utilizing XyDPA's superior function as an artificial FMN cyclase and phenothiazine as an electron donor able to quench the fluorescence of an isoalloxazine ring, PTZ-DPA enabled selective fluorescent discrimination of flavins (FMN, FAD, and RF): FAD shows ON(+), FMN shows OFF(-), and RF shows NO(0) fluorescence changes upon the addition of PTZ-DPA. With this selective sensing property, PTZ-DPA is applicable to real-time fluorescent monitoring of riboflavin kinase (RF to FMN), alkaline phosphatase (FMN to RF), and FAD synthetase (FMN to FAD).