Binding of Phenothiazines to bovine hemoglobin

Phenothiazines with bovine hemoglobin give solid complexes in phosphate buffer; this is due to the presence of ion-pairs between phenothiazines and phosphates. Using diluted solutions the number of sites available on each protein molecule and the intrinsic binding constants are determinated; the number of sites, in solutions and in solid complexes, is about the same for each drug, but different for the various phenothiazines.