RESONANCE RAMAN EVIDENCE FOR CHARGE-TRANSFER INTERACTIONS OF PHENOLS WITH THE FLAVIN MONO-NUCLEOTIDE OF OLD YELLOW ENZYME

During the reaction of various flavoenzymes with substrates, nonsemiquinone-type intermediates often appear and show a broad absorption band at longer wavelengths. These reaction intermediates are usually assigned to charge-transfer complexes of oxidized or reduced enzymes with substrate or product, but the details are not clear. In the case of Old Yellow Enzyme (NADPH oxidoreductase, EC 9.6.99.1) (OYE) which has a flavin mononucleotide (FMN) per monomer, many phenolic compounds are bound tightly to OYE when the flavin is in the oxidized state, giving rise to a long wavelength absorption in the same manner as the reaction intermediates,1 and a systematic correlation exists between λmax of the complexes and apam of Hammet constant of the para substituents of phenol.2 Existence of such correlation suggests that the phenol is the charge-transfer donor and oxidized flavin of the enzyme is the acceptor. Although phenols are inhibitors of the enzymatic reaction, physicochemical investigation of the complexes is substantially necessary to determine chemical properties of the coenzymes and also to elucidate the catalytic mechanism of the enzymatic. © 1979, American Chemical Society. All rights reserved.