Structural studies of iron and cobalt tetrasulfonated phthalocyanine-globin complexes

Area of Science:

• Biochemistry
• Biophysical Chemistry
• Coordination Chemistry

Background:

• Phthalocyanines are macrocyclic compounds with diverse applications.
• Globin proteins, like hemoglobin, are crucial for oxygen transport.
• Investigating metalloprotein complexes aids understanding of biological processes.

Purpose of the Study:

• To elucidate the structural and electronic properties of iron and cobalt tetrasulfonated phthalocyanine-globin complexes.
• To compare these synthetic complexes with natural hemoproteins.
• To determine the nature of subunit interactions and metal ion electronic states.

Main Methods:

• Circular dichroism (CD) spectroscopy to analyze protein secondary structure and electronic transitions.
• Electron paramagnetic resonance (EPR) spectroscopy to probe the electronic states of metal ions.
• Polyacrylamide gel electrophoresis (PAGE) for molecular weight estimation and complex characterization.

Main Results:

• Complexes exist as dimers in solution.
• Incorporation of metallophthalocyanines into apohemoglobin increases helical content and induces Cotton effects.
• CD and EPR studies reveal subunit inequivalence in the iron complex and confirm electronic similarities between cobalt complexes and natural coboglobins.
• The oxygen adduct of the cobalt complex is characterized as a superoxide coordinated to cobaltic phthalocyanine.

Conclusions:

• Tetrasulfonated phthalocyanine-globin complexes serve as valuable models for metalloproteins.
• The observed subunit inequivalence in the iron complex suggests structural heterogeneity.
• The cobalt complex's oxygen adduct provides insights into oxygen binding mechanisms in related systems.