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Iron hemiporphycene as a functional prosthetic group for myoglobin
Saburo Neya1, Kiyohiro Imai, Hiroshi Hori
1Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences, Chiba University, Inage-Yayoi, Japan. sneya@p.chiba-u.ac.jp
Inorganic Chemistry
|March 4, 2003
Summary
Researchers reconstituted myoglobin with hemiporphycene, a novel iron complex, to study its ligand binding. The modified myoglobin showed altered oxygen and carbon monoxide affinities, indicating changes in the heme pocket environment.
Area of Science:
- Biochemistry
- Bioinorganic Chemistry
- Protein Engineering
Background:
- Myoglobin is a crucial protein for oxygen transport and storage.
- Heme proteins, like myoglobin, contain an iron atom coordinated within a porphyrin ring.
- Novel porphyrinoid structures offer opportunities to modulate heme protein function.
Purpose of the Study:
- To investigate the ligand binding properties of an iron complex of hemiporphycene, a hybrid porphyrinoid.
- To reconstitute apomyoglobin with hemiporphycene and assess its functional characteristics.
- To understand how the unique structure of hemiporphycene influences the iron atom's coordination and reactivity within the myoglobin pocket.
Main Methods:
- Reconstitution of apomyoglobin with stoichiometric amounts of ferric hemiporphycene.
- Spectroscopic analysis (e.g., infrared absorption, electron paramagnetic resonance) to characterize the reconstituted protein.
- Ligand binding assays to determine affinities for cyanide, imidazole, fluoride, O(2), CO, and NO.
- Functional studies at physiological conditions (pH 7.4, 20°C).
Main Results:
- Successful reconstitution of apomyoglobin with ferric hemiporphycene, maintaining native-like iron coordination.
- Comparable binding affinities for cyanide, imidazole, and fluoride as native myoglobin.
- Reversible binding of O(2) and CO by ferrous hemiporphycene myoglobin, with a 12-fold higher O(2) affinity and slightly lower CO affinity.
- Altered coordination state (mixed 5- and 6-coordinate) for NO binding compared to native myoglobin.
- Evidence of core deformation influencing spectroscopic properties and ligand interactions.
Conclusions:
- Hemiporphycene incorporation into myoglobin alters the electronic properties of the iron center.
- The asymmetric hemiporphycene core affects O(2) and CO binding discrimination, potentially due to increased sigma-bonding in the Fe(II)-O(2) bond.
- The hemiporphycene structure destabilizes NO binding and influences iron-pyrrole interactions, leading to functional anomalies.