Deoxy-Hb is a tetramer of 2 alpha and 2 beta subunits, each with a bound heme. This is the structure that appears to the right.
The heme in deoxy-Hb is buried in a hydrophobic pocket. The Fe2+ ion in the heme is ligated to 4 pyrole N of the protoporphyrin ring, and a proximal His (F8) from the Hb. In addition, a distal His (E7), Val (E11) and Phe (CD1) surround the heme, as shown below. Bound CO occupies the other axial position in the structure to the right.
Notice how the 4 hemes are bound in deep pockets on each hemoglobin subunit. Also note that the proprionate groups of the heme are solvent exposed.
Mb and the beta-subunit of Hb (click twice if necessary)
The alpha and beta chains of hemoglobin have extensive tertiary structure identify with the single chain of Hb. The model ot the right shows the
backbone of the beta chain of hemoglobin in red and the backbone of myoglobin in green. Observe their extensive structural homology. (Superposition made using Swiss-PDP-Viewer)
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Atoms and Bonds