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Related Experiment Videos

The heme environment in barley hemoglobin

T K Das1, H C Lee, S M Duff

  • 1Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, USA.

The Journal of Biological Chemistry
|February 6, 1999
PubMed
Summary

Barley hemoglobin (Hb) features a unique heme environment with bis-imidazole coordination. Strong hydrogen bonding stabilizes bound oxygen, significantly reducing its dissociation rate compared to myoglobin.

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Area of Science:

  • Biochemistry
  • Spectroscopy
  • Protein Structure

Background:

  • Heme proteins like hemoglobin (Hb) play crucial roles in oxygen transport.
  • Understanding the heme environment is key to elucidating protein function and stability.

Purpose of the Study:

  • To investigate the heme environment and ligand structure in barley Hb.
  • To characterize the coordination and hydrogen bonding interactions within barley Hb.

Main Methods:

  • Resonance Raman spectroscopy
  • Electron paramagnetic resonance (EPR) spectroscopy
  • Analysis of CO complex vibrational frequencies (Fe-CO and C-O stretching)

Main Results:

  • Barley Hb exhibits bis-imidazole heme coordination without imidazolate character.

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  • Two distinct Fe-CO stretching modes (534 and 493 cm-1) were observed, pH-dependent.
  • The 534 cm-1 mode indicates hydrogen bonding of CO to the distal histidine, supported by a deuterium shift and a C-O stretch at 1924 cm-1.
  • The 493 cm-1 mode corresponds to an open heme pocket conformation, dominant under acidic conditions.

    • Conclusions:

    • A strong hydrogen bond exists between the distal histidine and bound CO in barley Hb.
    • This interaction likely stabilizes bound oxygen in the oxy derivative, enhancing stability.
    • Barley Hb shows a significantly reduced oxygen dissociation rate compared to sperm whale myoglobin.