Time resolved fluorescence of flavin adenine dinucleotide

From a comparison of the quatum efficiencies and lifetimes of the isoalloxazine fluorescence in flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) and from the slightly different extinction coefficients of both compounds Spencer and Weber have calculated and approximated the rate constants which describes the strong intramolecular quenching in FAD [ll. One of the assumptions in their derivation is that the observed fluorescence is due to the open or unstacked form of FAD, while the closed or stacked structures have no appreciable fluorescence. These assumptions are among others based on the experimental fact that the shape of the fluorescence spectra of FAD and FMN is almost identical. However, one can also approach this point from another direction. Suppose that the more complete kinetic scheme can be applied for FAD (fig. 1).