Interaction between cytochrome b(2) core and flavodehydrogenase from the yeast Hansenula anomala

The binding of cytochrome b(2) core (a monomer) to flavodehydrogenase (a tetramer), both purified from Hansenula anomala flavocytochrome b(2), has been studied in the presence of 2-p-toluidinylnaphthalene-6-sulfonate (TNS). The association constant of the TNS-flavodehydrogenase complex was found to be equal to 0.64 mu M-1 with a stoichiometry of one TNS per tetramer, Binding of cytochrome b(2) core to flavodehydrogenase was followed by monitoring changes in the TNS fluorescence, Our results indicated that the binding is cooperative, with a stoichiometry of four cytochrome b(2) cores per tetramer of flavodehydrogenase.