title: Reduction of lactoperoxidase-H2O2 compounds by ferrocyanide: indirect evidence of an apoprotein site for one of the two oxidizing equivalents.
abstract: The titration by ferrocyanide and the localization of the oxidizing equivalents of lactoperoxidase "compound II" were studied as a function of pH. It was demonstrated that 1) whatever the pH, the structure of lactoperoxidase "compound II" was compatible with a Fe IV R degree state, 2) at acidic pH, ferrocyanide preferentially reduced the oxidizing equivalent localized on the heme iron to give an Fe III R degree compound, 3) at pH 4.2 only the Fe III R degree form was obtained after reduction of lactoperoxidase "compound II" with one mole of ferrocyanide and whereas at pH greater than 4.2, a mixture of both Fe III R degree and Fe IV R forms was present, 4) lowering the pH from 7.2 to 4.0 induced a transition of Fe IV R state to Fe III R degree state, but increasing the pH from 4.0 to 7.2 did not permit the formation of Fe IV R compound from Fe III R degree compound.
mesh_terms: D001051:Apoenzymes; D001059:Apoproteins; D001665:Binding Sites; D005295:Ferrocyanides; D006861:Hydrogen Peroxide; D006863:Hydrogen-Ion Concentration; D007201:Indicator Dilution Techniques; D007700:Kinetics; D007784:Lactoperoxidase; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010544:Peroxidases
chemical_list: D001051:Apoenzymes; D001059:Apoproteins; D005295:Ferrocyanides; D006861:Hydrogen Peroxide; D007784:Lactoperoxidase; D010544:Peroxidases