Reduction of lactoperoxidase-H2O2 compounds by ferrocyanide: indirect evidence of an apoprotein site for one of the two oxidizing equivalents.
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.
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
D001051:Apoenzymes; D001059:Apoproteins; D005295:Ferrocyanides; D006861:Hydrogen Peroxide; D007784:Lactoperoxidase; D010544:Peroxidases