Fِrster energy transfer from tryptophan to flavin in glucose oxidase enzyme

The difference in the properties of the tryptophan fluorescence of the hologlucose oxidase forms, as compared to those of the apoprotein, can unambiguously be interpreted as due to a Fِrster energy transfer from the tryptophan residues to the flavinic group. Indeed, the atomic absorption of a glucose oxidase solution shows that the enzyme is not associated to any metals which could be responsible for the tryptophan fluorescence quenching effect. The data show that only 7 Trp residues are partially coupled to the flavin group and that the strength of this coupling is dependent on the flavin redox state.