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The Biochemical journal1971; 124(1); 31-45; doi: 10.1042/bj1240031

The binding of carbon dioxide by horse haemoglobin.

Abstract: 1. Three modified horse haemoglobins have been prepared: (i) alpha(c) (2)beta(c) (2), in which both the alpha-amino groups of the alpha- and beta-chains have reacted with cyanate, (ii) alpha(c) (2)beta(2), in which the alpha-amino groups of the alpha-chains have reacted with cyanate, and (iii) alpha(2)beta(c) (2), in which the two alpha-amino groups of the beta-chain have reacted with cyanate. 2. The values of n (the Hill constant) for alpha(c) (2)beta(c) (2), alpha(2)beta(c) (2) and alpha(c) (2)beta(2) were (respectively) 2.5, 2.0 and 2.6, indicating the presence of co-operative interactions between the haem groups for all derivatives. 3. In the alkaline pH range (about pH8.0) all the derivatives show the same charge as normal haemoglobin whereas in the acid pH range (about pH6.0) alpha(c) (2)beta(c) (2) differs by four protonic charges and alpha(c) (2)beta(2), alpha(2)beta(c) (2) by two protonic charges from normal haemoglobin, indicating that the expected number of ionizing groups have been removed. 4. alpha(c) (2)beta(2) and alpha(c) (2)beta(c) (2) show a 25% decrease in the alkaline Bohr effect, in contrast with alpha(2)beta(c) (2), which has the same Bohr effect as normal haemoglobin. 5. The deoxy form of alpha(c) (2)beta(c) (2) does not bind more CO(2) than the oxy form of alpha(c) (2)beta(c) (2), whereas alpha(c) (2)beta(2) and alpha(2)beta(c) (2) show intermediate binding. 6. The results reported confirm the hypothesis that, under physiological conditions, haemoglobin binds CO(2) through the four terminal alpha-amino groups and that the two terminal alpha-amino groups of alpha-chains are involved in the Bohr effect.
Publication Date: 1971-08-01 PubMed ID: 5166592PubMed Central: PMC1177110DOI: 10.1042/bj1240031Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research looks into how changes in horse haemoglobin affect its ability to bind with carbon dioxide. It specifically examines three types of modified horse haemoglobin, where only certain parts of the haemoglobin molecule interact with cyanate. The study ultimately supports the hypothesis that haemoglobin binds with CO2 through alpha-amino groups, some of which also appear to be involved in the Bohr effect.

Methods and Materials

  • The researchers created three types of modified horse haemoglobin. Each type had specific interactions with cyanate, a compound that can chemically modify proteins.
  • The first type was alpha(c) (2)beta(c) (2), where both the alpha and beta chains of the molecule had reacted with cyanate.
  • The second was alpha(c) (2)beta(2), where the alpha-amino groups of the alpha-chains had reacted with cyanate.
  • Lastly, the third was alpha(2)beta(c) (2), where the alpha-amino groups of the beta chain had reacted with cyanate.

Hill Constant

  • They examined the Hill constant (a measure of cooperative binding in molecules) of the three modified haemoglobins. The values were 2.5, 2.0, and 2.6 respectively, indicating the existence of cooperative interactions between the haem groups for all derivatives.

pH Effects on Charge and Ionizing Group Removal

  • At a slightly alkaline pH (around pH 8.0), all versions maintained the same charge as normal haemoglobin. However, in acidic conditions (around pH 6.0), significant differences were seen. The alpha(c) (2)beta(c) (2) molecule varied by four protonic charges and the alpha(c) (2)beta(2) and alpha(2)beta(c) (2) molecules by two charges in comparison to normal haemoglobin.
  • This difference in protonic charges suggests that the expected number of ionizing groups in the haemoglobin molecules were removed during the experiment.

Impact on Bohr Effect

  • The alpha(c) (2)beta(2) and alpha(c) (2)beta(c) (2) variants showed a 25% decrease in the alkaline Bohr effect as opposed to alpha(2)beta(c) (2), which maintained the same Bohr effect as unmodified haemoglobin.
  • The Bohr effect refers to haemoglobin’s decreased affinity for oxygen under conditions of lower pH, essentially how it responds to changes in the acidity or alkalinity of the environment.

CO2 Binding

  • The alpha(c) (2)beta(c) (2) variant didn’t bind more CO2 in its deoxy form than it did in its oxy form. The other two variants showed intermediate binding capabilities. This indicates the role of the alpha-amino groups in CO2 binding.

Conclusion

  • The results upheld the hypothesis that haemoglobin binds CO2 through the four terminal alpha-amino groups and the two terminal alpha-amino groups of alpha-chains are involved in the Bohr effect.

Cite This Article

APA
Kilmartin JV, Rossi-Bernardi L. (1971). The binding of carbon dioxide by horse haemoglobin. Biochem J, 124(1), 31-45. https://doi.org/10.1042/bj1240031

Publication

ISSN: 0264-6021
NlmUniqueID: 2984726R
Country: England
Language: English
Volume: 124
Issue: 1
Pages: 31-45

Researcher Affiliations

Kilmartin, J V
    Rossi-Bernardi, L

      MeSH Terms

      • Amino Acids / analysis
      • Animals
      • Autoradiography
      • Carbon Dioxide
      • Carbon Isotopes
      • Carbon Monoxide
      • Chromatography
      • Cyanates / metabolism
      • Heme
      • Hemoglobins
      • Horses
      • Hydrogen-Ion Concentration
      • Peptides / analysis
      • Protein Binding
      • Sulfur Isotopes

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      Citations

      This article has been cited 31 times.