Hemoglobin distal histidine

Figure 4.12 Distal histidine hydrogen bonding structure for hemoglobin (left) and a heme model (right). (Reprinted with permission from Figure 12 of Momenteau, M. Reed, C. A. Chem. Rev., 1994, 94, 659-698. Copyright 1994, American Chemical Society.)...

There is no counterpart to the distal histidine of myoglobin in hemoglobin. 

Comparison of the primary sequences of hemoglobin chains from more than 60 different species reveals that only nine residues in the polypeptide chain are invariant (i.e. the same) between all of the species. These nine residues include the proximal and distal histidines which are essential for the correct functioning of the protein. Many of the other residues are replaced from one species... 

Model hemes coordinated to phenoxides and aryl thiolates have been investigated as models of catalase and hemoglobins M (which have tyrosine substituted for either the proximal or distal histidine) and cytochromes P450 (which have the thiolate of cysteine coordinated to... 

Figure 7.27 Stabilizing free o-hemoglobin. The structure of a complex between AH.SP and -hemoglobin is shown. In this complex, the iron atom is bound to oxygen and to the distal histidine. Notice that AHSP binds to the same surface of a-hemoglobin as does p-hemoglobin. [Drawn from lYOl.pdb.]...

Fe to shift into the ring center. The proximal histidine in the Fe coordination sphere (see Fig, lb) also moves and acts as a means of communicating between sub-units. Another feature of hemoglobin is designed to lessen its affinity for other ligands. The position of the distal histidine shown in Fig. lb forces coordination in a nonlinear geometry. This is favorable for 02 but not for strongly... 

Olson JS, Mathews AJ, Rohlfs RJ, Springer BA, Egeberg KD, Sligar SG, Tame J, Renaud JP, Nagai K (1988) The role of the distal histidine in myoglobin and hemoglobin. Nature 336 265-266... 

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