ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
In this paper we have suggested that the interaction between the hemes of hemoglobin is due primarily to entropy effects associated with configurational changes in the molecule as a whole. In hemoglobin the four hemes appear to occur in paris, and the estimated interaction between members of the same pair would correspond to an entropy effect of 12 calories per degree or more, which is roughly the same as the entropy change which occurs when a mass of rubber equal to the half weight of hemoglobin is stretched to between twice and three times its initial length. Such an entropy change would account for the value of n = 1.9 observed in the oxygen and oxidation equilibria of hemoglobin split in halves by urea. The configurational hypothesis here proposed would at once explain the close similarity between the oxygen, carbon monoxide, and oxidation equilibria of intact hemoglobin, for x-ray studies indicate that the same configurational changes accompany all three reactions. It would also account for the difference of solubility between hemoglobin and oxyhemoglobin, as well as a number of other matters. Some new data on the oxygenation of sickle-cell anemia hemoglobin are presented and discussed in connection with the hypothesis.The further suggestion is made that the Bohr effect may be due, not to changes of bond type in the heme globin linkage as proposed by Coryell and Pauling, but to changes in the position and environment of certain acid groups resulting from changes in the configuration of the hemoglobin molecular as a whole. This would explain the essential identity of the Bohr effect for oxidation, oxygenation, and combination with carbon monoxide, as well as other things.It is finally suggested that the kind of entropy effect postulated in hemoglobin may play a role in the activation of substrates by enzymes more generally.As we have pointed out, the suggestions made in this paper are highly speculative and their value will depend largely on the extent to which they point to new experiments. Among many questions which arise are these: Is there any configurational change which occurs in myoglobin, with only a single layer of polypeptide chain, when it is oxygenated? What happens to the interaction and the Bohr effect when hemoglobin is caused to combine with a variety of reagents which react with specific groups in the molecule? Is there any significant change in the dipole moment of the hemoglobin molecule when it combines with oxygen and changes shape? These and other questions, if they were answered, would be highly pertinent to the suggestions presented in this paper.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1951.120070506
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