Interaction of phenols with old yellow enzyme. Physical evidence for charge-transfer complexes.
Evidence is presented that the changes in absorption spectrum obtained on complex formation between Old Yellow Enzyme and phenolic compounds are due to charge-transfer interactions. The positive correlation between the energy of the long wavelength transition and the Hammett para constant with a series of para-substituted phenols indicates that the phenol is the charge-transfer donor and the oxidized flavin of the enzyme is the charge-transfer acceptor. The same conclusion is drawn from studies in which the flavin of the native enzyme, flavin mononucleotide, was replaced by a variety of artificial flavins of different oxidation-reduction potential. The effect of pH on the dissociation constant for the enzyme-ligand binding also indicates that it is the phenolate anion, rather than the conjugate acid, which is responsible for the charge-transfer interaction. The significance of these results is discussed relative to long wavelength absorbing species detected with other flavoproteins.
D001665:Binding Sites; D004579:Electron Transport; D004735:Energy Transfer; D005415:Flavins; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008433:Mathematics; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D009252:NADPH Dehydrogenase / Q000378:metabolism; D010636:Phenols / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship
D005415:Flavins; D010636:Phenols; D009247:NADH, NADPH Oxidoreductases; D009252:NADPH Dehydrogenase