The oxidation of sperm whale oxymyoglobin catalyzed by ferrocyanide ions

Specific catalytic oxidation of sperm whale oxymyoglobin by small amounts o f potassium ferri- and ferrocyanide, from 1 to 20% in relation to the prote in concentration, was studied. The mechanism of catalysis was shown to invo lve specific binding of the ferrocyanide anion to the protein. The influenc e of pH and ionic strength of the medium, the [Fe(CN)(6)](4-) concentration and of chemical modification of Mb histidines by bromoacetate, as well as the effect of the Mb complexing with redox-inactive zinc ion on the rate of reaction was examined. The zinc ion forms a stable complex with His 119(GH 1) on the Mb surface at the equimolar Zn2+ concentration. The kinetic schem e of the reaction was analyzed, and the equilibrium and kinetic parameters were obtained. It was first shown that the strong oxidant such as potassium ferricyanide is able to react with the same protein by two distinct mechan isms: (i) a simple outer sphere electron transfer over the heme edge and (i i) electron transfer after the specific binding of [Fe(CN)(6)](4-) to oxyMb in the His 119(GH1) region, thus catalyzing the protein oxidation.