Abstract
Absorption spectrum of partly reduced flavin mononucleotide in hydrochloric acid solution was analyzed and the value of the “effective semiquinone formation constant” (K) was estimated by a graphical method. By using the value of K, absorption spectrum of semiquinone was determined. It was found that flavin mononucleotide semiquinone has two absorption maxima, at 350 and 490 mlt, and that the extinction coefficients at these wavelengths are 10.0×103 (350mμ) and 9.4×103M-1cm.-1 (490mμ), respectively.
Although the K-value increased with the increasing hydrogen ion concentration, the absorption spectrum of FMN semiquinone was the same irrespective of the hydrogen ion concentration within the pH range tested.
The authors wish to express their gratitudes to Dr. T. Yamada for his valuable discussions.
