The reactivities of the liganded states of the embryonic haemoglobins of the mouse with both O2 and CO were measured and compared with the reactivities of the adult protein. Laser-photolysis experiments on the recombination of O2 with the partially oxygenated proteins indicates chain heterogeneity in the adult and embryonic EII and EIII species, with the difference in subunit reactivity being greatest in the embryonic species. Haemoglobin EI shows chain equivalence in these experiments. The homogeneous time courses observed for the O2-dissociation reactions are consistent with chain equivalence within all the proteins with regard to this reaction. The specific values obtained for the respective rate constants from each of these studies indicates that the high O2 affinity previously reported for haemoglobin EI is, in greatest part, due to its low O2 dissociation rate. Flash-photolysis studies on the binding of CO with the partially liganded forms of the proteins show the same patterns of chain heterogeneity as seen in O2-binding studies.
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