Assignment of the quaternary structure of FeZn hybrid hemoglobins: Implications for allosteric theories

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Abstract

The quaternary structures of α2Znβ2Fe(III), α2Znβ2Fe(III)N3, α2ZnβFe(II)CO, α2Fe(III)β2Zn, α2Fe(III)N3β2Zn and α2Fe(II)COβ2Zn have been assigned using U.V. Circular dichroism, subunit dissociation measurements, and ligand binding rates. A “T” structure is obtained for all these ZnFe hybrids. These results suggest that a complete R → T quaternary structure change does not occur until the third ligand binds. These observations, combined with previous studies of mixed valence Hb hybrids, place severe constraints on two state models of hemoglobin allostery.

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