Stability properties of sperm whale oxymyoglobin

Sperm whale oxymyoglobin was isolated directly from muscle and was examined for its stability properties over the wide range of pH 5-13 in 0.1 M buffer at 25 degrees C. The remarkable pH dependence for the autoxidation rate was analyzed using the kinetic equation derived in terms of nucleophilic displacement processes of O-2 from oxymyoglobin by the entering water molecule or hydroxyl ion with the iron resulting in the ferric form. Most of the autoxidation reaction of the oxymyoglobin can be best explained by the proton-catalyzed processes involving the distal histidine as the catalytic residue. The kinetic equation could also be used as an interesting diagnostic probe into differences in the heme reactivity and the heme environment of different types of oxymyoglobin from other sources.