FLASH PHOTOREDUCTION OF FLAVIN MONO NUCLEOTIDE IN NEUTRAL SOLUTIONS ABSOLUTE ABSORPTIVITY OF THE SEMIQUINONE

Abstract

Abstract— Flash photoreduction of FMN, in aqueous solutions (pH 5–9) leads to the semiquinone (FMNH or FMN). The yield of semiquinone was determined by measuring the amount of leuco‐FMN (FMNH 2 or FMNH‐) formed in the subsequent disproportionation. The absorption spectrum of the semiquinone, previously known in relative units, has been converted to an absolute basis. Revised values are given for the protolysis constant for FMNH, for the disproportionation rate, and for the formation constant K F . It is found that K F is much lower for the anionic than for the neutral form of the semiquinone.