HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Tomita, S. Articles by Riggs, A. Search for Related Content PubMed PubMed Citation Articles by Tomita, S. Articles by Riggs, A. Social Bookmarking                      What's this?

Studies of the Interaction of 2,3-Diphosphoglycerate and Carbon Dioxide with Hemoglobins from Mouse, Man, and Elephant

From the ¹ From the Department of Zoology, University of Texas, Austin, Texas 78712

The oxygen affinity of mouse hemoglobin is greatly lowered by 2,3-diphosphoglycerate (2,3-DPG). The higher the pH, the smaller the size of the effect. The pH dependence of this shift in log p₅₀ resembles a titration curve with an apparent pK of 7.76. This value is close to that reported for the -NH₂ groups of deoxyhemoglobin.

The addition of 1 to 2 moles of 2,3-DPG per mole of hemoglobin decreases the value of n in Hill's equation. Further addition causes n to return to normal values. However, estimation of the overall free energy of interaction shows that 2,3-DPG does not affect interaction. The changes in n are therefore believed either to reflect the presence of mixtures of hemoglobins combined to varying extents with 2,3-DPG or the fact that the free 2,3-DPG concentration is continuously increasing during oxygenation.

The Bohr effects at 20°, between pH 7.0 and 7.5, of hemoglobins from mouse, man, and elephant are approximately -0.52, -0.48, and -0.30, respectively; these values become -0.9, -0.7, and -0.44, respectively, in the presence of 1 mole of 2,3-DPG per mole of hemoglobin.

Carbon dioxide abolishes the effect of 2,3-DPG on the oxygen equilibrium of mouse hemoglobin at pCO₂ = 60 mm Hg, pH 7.3, and 20°. The higher the pCO₂ the lower is the pH at which CO₂ abolishes the 2,3-DPG effect.

Mouse hemoglobin digested with carboxypeptidase A is devoid of a 2,3-DPG effect. In contrast, the oxygen equilibrium of hemoglobin digested with carboxypeptidase B shows a 2,3-DPG effect.

We conclude that 2,3-DPG binds at the same sites as does CO₂, namely at the NH₂-termini of the and ß chains, but that interaction of 2,3-DPG with the ß chain is functionally the most important.

Mechanisms are proposed to explain both the effects of CO₂ and of 2,3-DPG. The CO₂, bound as carbamate (-NHCOO^-), and the 2,3-DPG anion are both believed to reduce the oxygen affinity because the introduction of the negative charge interferes with the conformation change associated with oxygenation.

We conclude that hemoglobins from different mammals are not physiologically equivalent and do not by themselves provide support for the theory of selectively neutral mutations. Instead, the properties of the oxygen equilibria of mammalian hemoglobins appear to reflect an adaptation of the metabolic needs of the animal.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				X. Xu, V. L. Lockamy, K. Chen, Z. Huang, H. Shields, S. B. King, S. K. Ballas, J. S. Nichols, M. T. Gladwin, C. T. Noguchi, et al. Effects of Iron Nitrosylation on Sickle Cell Hemoglobin Solubility J. Biol. Chem., September 20, 2002; 277(39): 36787 - 36792. [Abstract] [Full Text] [PDF]