JBC, Vol. 253, Issue 23, 8554-8558, Dec, 1978
The sensitivity of hemoglobin oxygen affinity to diphosphoglycerate and the characteristic pH of methemoglobin
O. Amire, G. B. Ogunmola and J. G. Beetlestone
The sensitivity of the oxygen affinity of a hemoglobin to
2,3-diphosphoglyceric acid concentration has been defined as the change in
log1/2O2 (deltalogp1/2O2) which results from saturating the hemoglobin with
2,3-diphosphoglyceric acid. The sensitivity varies from one hemoglobin
species to another and is linearly rated to the difference in the logarithm
of the binding constants of 2,3-diphosphoglyceric acid to deoxy- and
oxyhemoglobin, the characteristic pH (pHch), and inversely proportional to
the magnitude of the alkaline Bohr effect measured in a saturating amount
of 2,3-diphosphoglyceric acid. Its magnitude is higher in large animals
than in small animals and varies linearly with the charged amino acid
composition of the hemoglobin. The charged amino acid residues must have
been selected for in mammals with high metabolic needs and against in
animals with low metabolic needs. Variability in the effect of
2,3-diphosphoglyceric acid on the oxygen transport in the different animal
hemoglobins must therefore be the result of a positive Darwinian Selection
of the charged amino acid residues in their hemoglobins. Furthermore, all
the charged groups and not those at the binding site alone, affect the
2,3-diphosphoglyceric acid binding constant of a hemoglobin.
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