The structure of hydrophobic cores of globins.

The contacts between bulky hydrophobic side chains (Val, Leu, Ile, Met, Phe, Tyr, and Trp) were studied in five globins with known three-dimensional structures. It is shown that a large majority of these side chains participate in such contacts, where most often one side chain makes contact with two to four nearby side chains. The "recognition element" of a helical region is most often a pair of bulky hydrophobic side chains belinging to neighboring turns of an alpha-helix. Such pairs most often make contact with bulky hydrophobic side chains brought in from the outside. An analysis is made of contacts between the hydrophobic side chains common to all five globins. It is shown that as a rule the most intense contacts in each globin are also common to the five globins. The role of these invariant contacts in the formation of the tertiary structure of globin molecules is considered. A suggestion is made that the apoglobin molecule consists of independently self-organizing halves, the internal structure of which is less subject to fluctuation than their mutual arrangement.