A study of the interaction between two proteins, one containing a flavin mononucleotide

Interaction between cytochrome c and flavocytochrome b2 has been studied in presence of 2-p-toluidinylnaphthalene-6-sulfonate (TNS). Affinity of the probe to flavocytochrome b2 increases when the complex between the two proteins is obtained. Binding of TNS increases the fluorescence of flavocytochrome b2 FMN. When the stoichiometry of the complex between the two proteins is reached, TNS looses its affinity and stops binding on the flavocytochrome b2; consequently, FMN fluorescence increase is no more observed. The dissociation constant of the complex was found equal to 0.1 microM. A similar result was obtained for the interaction between cytochrome c and flavodehydrogenase domain. The latter was obtained by proteolysis of flavocytochrome b2.