Sperm-whale myoglobin has been fractionated by isoelectric focusing in Sephadex gels, and oxygen and CO ligand association and dissociation kinetics were measured by stopped-flow and flash photolysis for the eight most abundant fractions. Except for the association rate for CO binding, there appeared to be no significant differences in rates among the various bands for a given reaction. Rates for oxygen dissociation and association determined by replacement reactions were in good agreement with rates determined with dithionite and by flash photolysis, respectively. The rate for CO dissociation determined by NO replacement was homogeneous. Heterogeneous kinetics were observed for the dissociation reaction when Fe(CN)63 was used. An evaluation of M, the Oo-CO partition constant, from the kinetic data was in excellent agreement with a direct equilibrium determination.
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