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Hemoglobin, pH and DPG/chloride shifting.

Massimo Pomponi1, Enrico Gavuzzo, Claudia Bertonati

  • 1Istituto di Biochimica, UCSC, Facoltà di Medicina, Largo F, Vito 1, 00168 Rome, Italy. m.pomponi@rm.unicatt.it

Biochimie
|January 26, 2005
PubMed
Summary

Polar bear hemoglobin shows reduced DPG response due to chloride binding. This adaptation in Ursus maritimus hemoglobin may be linked to extreme environments and acidosis, not just temperature.

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Area of Science:

  • Biochemistry
  • Physiology
  • Evolutionary Biology

Background:

  • Hemoglobin's oxygen-binding properties are modulated by various factors, including DPG and chloride ions.
  • Adaptations in hemoglobin function are crucial for animals living in extreme environments.
  • Previous studies suggested DPG/chloride shifting in ruminants and questioned temperature as the sole driver for such mechanisms.

Purpose of the Study:

  • To investigate the decreased 2,3-diphosphoglycerate (DPG) response in polar bear (Ursus maritimus) hemoglobin.
  • To understand the role of chloride binding in polar bear hemoglobin function and its evolutionary implications.
  • To explore potential mechanisms explaining hemoglobin adaptations in animals from extreme habitats.

Main Methods:

  • Comparative analysis of polar bear hemoglobin structure and function against human hemoglobin A (HbA).

Related Experiment Videos

  • Identification of specific amino acid substitutions in polar bear beta chains.
  • Hypothesizing the functional impact of structural changes on chloride and DPG binding.

    • Main Results:

    • Polar bear hemoglobin exhibits a decreased DPG response, interpreted as DPG/chloride shifting.
    • Specific chloride-binding sites were identified in polar bear Hb, located between Lys-76 (beta) and Lys-8 (beta).
    • Amino acid substitutions (Pro-5 (A2)--> Gly and Ala-76 (E20)-->Lys) in beta chains increase central cavity flexibility and create a chloride-binding site.

    Conclusions:

    • The observed DPG/chloride shifting in polar bear hemoglobin is likely an adaptation to extreme environmental conditions, potentially related to acidosis during food shortage.
    • Specific amino acid substitutions facilitate chloride binding, influencing oxygen-binding affinity.
    • This mechanism highlights the diverse evolutionary strategies employed by mammals to adapt hemoglobin function to challenging habitats.