The monomeric hemoglobin fraction from Glycera dibranchiata, the blood worm, has been fractionated into four components. Rate constants and activation energies have been measured for 02 and CO association and dissociation reactions for the three most abundant monomeric hemoglobins. Hemoglobin I appears to have the largest 02and CO association and 02 dissociation rate constants yet reported for a hemoglobin. Hemoglobin II shows very similar kinetics. The values for M, the 02-CO partition constant, for these two components appear to be the largest for any hemoglobin. The CO and 02 association and 02 dissociation rate constants for hemoglobin III, the most basic of the three major monomeric hemoglobins, are about one-sixth to one-eighth those for hemoglobins I and II, a striking example of functional heterogeneity. On the other hand, oxygen equilibrium constants are very similar for the three hemoglobins. It appears that hemoglobin II corresponds to that hemoglobin for which the sequence has been reported. The unusually rapid ligand kinetics are thus associated with the substitution of the distal histidine by leucine. in all cases, the monomer ligand kinetics were monophasic, in contrast to earlier results [Seamonds, B., McCray, J. A., Parkhurst, L. J., & Smith, P. D. (1976) J. Biol. Chem. 251, 2579], The 02 and CO association ligand kinetics for the polymer were at least biphasic. The rates for the faster component were similar to those for hemoglobin III of the monomer and about four times faster than the rates for the slower polymeric component. CO dissociation was monophasic for the polymer. Analysis of the 02-C0 relaxation data suggests that there is very little heterogeneity in the 02 dissociation reaction for the polymeric component.
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