On the Nature of Compounds Present in Mixtures of Oxidized and Reduced Flavin Mononucleotides

摘要

The composition of the equilibrium mixtures obtained on mixing known amounts of flavin mononucleotide (FMN) and reduced FMN (FMNH2) were studied by spectrophotometry, fluorimetry, and E.S.R. spectrometry. The major component of the mixtures containing more than 2mM total flavin is a species absorbing at 900 millimicrons which we regard as a charge transfer complex between FMNH2 and FMN. Comparison of the spectrophotometric and E.S.R. data show a close correlation between the extinction at 570 millimicron and the concentration of free radical. When the radical concentration is plotted against total percentage of reduced flavin at constant flavin concentration, a strongly asymmetric curve is obtained, peaking at about 70% reduction. Evidence is presented that this asymmetry is due to the presence of another radical species, a complex between the semiquinone and FMNH2. The formation of the complex between semiquinone and FMNH2 is inhibited in the presence of solutes such as caffeine and urea and in various organic solvents. (Author)