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The heme environment in barley hemoglobin
1Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
The Journal of Biological Chemistry
|February 6, 1999
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.
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.
- 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.