Globin hydrophobic interior

The second condition controls the degree of exposure of the heme to the hemoprotein s external environment and access of ligands and substrates to its active site. Thus, heme buried deep within the hydrophobic interior of a globin apoprotein is ideally suited to the non-oxidative binding of oxygen. 

The most characteristic amino acid residue of the distal side is again the residue closest to the iron, the distal histidine (Figure 2). The globular structure of myoglobin is characteristic for all the globins and excludes the formation of large cavities in the protein interior. Since this is a mainly hydrophobic region very few structural water molecules were located inside the protein. Polar... 

The globin protein provides an example of particular interest to the present discussion. As stated by Perutz, Ionized residues are excluded from the interior of globin chains, which is filled largely by hydrocarbon side chains, but some serines and threonines also occur there. This perspective immediately emerged from the first few protein structmes determined by X-ray diffraction methods. As many more protein structures have been so determined, the only essential modification of this quotation is that whenever charge is found buried within the hydrophobic associations, it is always found ion paired (also referred to as a salt bridge). This is, of course, as required by the... 

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