Conformation Are Initiated by Oxygen Binding

A close-up view of the iron-porphyrin complex with the F helix in deoxyhemoglobin. Note that the iron atom is displaced slightly above the plane of the porphyrin. (Illustration copyright by Irving Geis. Reprinted by permission.) 

Downward movement of the iron atom and the complexed polypeptide chain on binding oxygen. The structure is shown before (black) and after (blue) binding oxygen. Movement of His F8 is transmitted to valine FG5, straining and breaking the hydrogen bond to the penultimate tyrosine. Only the chain is shown here. 

The structural arguments advanced here to explain f oxygen binding by hemoglobin are supported by comparisons of the amino acid sequences of a and j8 chains for a large number of hemoglobins from different species. Data from 60 species of a chains and 66 species of )S chains 

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