RGI 7

Introduction to Myoglobin and ATP

• Myoglobin is crucial for oxygen storage and transport in muscle cells.

• ATP (Adenosine Triphosphate) synthesis requires oxygen.

Oxygen Transport Mechanism

• Oxygen is transported by red blood cells using heme, which is a critical component of myoglobin.

• The heme increases the molecular weight of myoglobin, facilitating its function as an oxygen carrier.

Structure of Myoglobin

• Protein Composition

  • Myoglobin is a globular protein chain.

  • The structure is classified as tertiary, which arises from secondary structures.

  • Primary structure consists of approximately 50 to 60 amino acids.

  • Peptide bonds (NH bonds) link these amino acids.

• Secondary Structure Formation

  • Myoglobin exhibits alpha-helix and beta-pleated sheet formations.

  • Hydrogen bonds maintain the structural integrity of the alpha helix.

  • The beta pleated structure features interactions between adjacent chains through hydrogen bonding.

• Tertiary Structure Development

  • Tertiary structure emerges from intermolecular interactions, including:

    • Salt bridges (electrostatic interactions between positively and negatively charged R groups).

    • Hydrophobic interactions where hydrophobic side chains cluster inward, away from the aqueous environment.

Heme Group Composition

• Structure of Heme Group

  • Heme consists of a porphyrin ring with an iron (Fe) atom at its center.

  • The porphyrin ring is a tetradentate planar ligand that coordinates with four nitrogen atoms.

  • This structure contributes to the binding affinity for oxygen.

• Function of Iron

  • The iron atom's coordination number is five, allowing one vacant site to bind oxygen.

  • The preservation of the Fe²⁺ ion is critical for oxygen binding.

  • This bivalent iron state (Fe²⁺) enables reversible oxygen binding, essential for myoglobin's function.

Interaction with the Aqueous Environment

• Hydrophobic Interior

  • The interior of the myoglobin globule is hydrophobic, protecting the Fe²⁺ from an aqueous environment.

  • Hydrophobic R groups of the amino acids are clustered inside the protein structure.

Crystal Field Splitting Energy (CFSE)

• D Orbital Arrangement

  • Transition metals like Fe have five d orbitals (dxy, dyz, dzx, dx2−y2, dz2).

  • Interaction with ligands leads to energy splitting of these orbitals, influencing electron pairing.

  • CFSE affects magnetic properties, determining whether complexes are paramagnetic (unpaired electrons) or diamagnetic (all paired).

• Effect of Coordination

  • When oxygen binds to myoglobin, the electron configuration stabilizes, reducing unpaired electrons and adjusting the electronic state of iron.

Hemoglobin Functionality and Structure

• Comparison with Myoglobin

  • Hemoglobin consists of four globin subunits, each binding one oxygen molecule; this allows for cooperative binding.

  • Deoxygenated hemoglobin is termed deoxymyoglobin, showcasing different electronic states and coordination configurations.

• Interunit Interaction

  • Salt bridges maintain interactions between subunits of hemoglobin.

  • Upon oxygenation, histidine and iron transition coordination, impacting the protein conformation for oxygen affinity.

Conclusion

• Myoglobin plays a vital role in oxygen storage and transport in muscle tissue, with a complex structure that allows for effective interaction with oxygen.

• Understanding the structure-function relationships in myoglobin and hemoglobin reveals insights into their biological significance.