What are the three functions of myoglobin?
- Facilitates oxygen diffusion through muscle tissue.
- Acts as a local reserve of oxygen during intense exercise.
- Stores oxygen in aquatic animals.
If K(d) is high, what does this mean for the concentration of ligand/protein in a solution?
K(d) is high = Lower concentrations of complexes compared to free-floating ligand and proteins.
If K(d) is low, what does this mean for the concentration of ligand/protein in a solution?
K(d) is low = Higher concentrations of complexes compared to free-floating ligand and proteins.
What is specificity?
Specificity is the interaction between protein and ligand in which a protein is specialized for interaction with that particular ligand.
What is affinity?
The strength and efficacy at which a ligand can bind to a protein.
What is the structure of myoglobin?
8 alpha-helices and irregular structures in a globular structure; 153 amino acids present in total. Heme prosthetic group appears in hydrophobic pocket to allow for binding of oxygen.
What is the structure of Heme?
Circular and planar porphyrin ring containing a ferrous (2+) ion situated between 4 nitrogen atoms. Two propionyl (charged polar) groups extend from the bottom of the porphyrin ring.
What compounds bind at the fifth and sixth binding site of the ferrous ion in Heme?
6: Histidine
5: Oxygen
What is the proximal histidine?
The histidine present in the 6th position relative to the ferrous ion of myoglobin (Known also as HisF8).
How is the Heme prosthetic group held in place?
Through hydrophobic inetractions and coordination of bonds between the ferrous ion and the proximal histidine.
What is the function of HisF8?
- Binds heme into heme-binding pocket.
2. Prevents oxidation of ferrous ion.
What is the distal histidine?
A histidine group (HisE7) that binds to the oxygen present at heme position 6.
What is the function of HisE7?
- Increase oxygen-binding affinity.
- Lower affinity for other molecules.
- Increase specificity for oxygen.
What is the structure of hemoglobin?
Tetramer with 2 alpha subunits, 2 beta subunits with a heme group present in each subunit.
What are homologous proteins?
Proteins that stem from similar ancestors, often contain similar or identical amino acids in key locations in the protein.
What are conservative substitutions?
Relatively minor effects on structure/function.
What are critical substitutions?
Changes in structure and function based on amino acid substitutions.
How is the binding curve of Myoglobin described?
As a hyperbolic curve.
How is the binding curve of hemoglobin described?
As a sigmoidal curve.
What are the two conformations of hemoglobin?
Tensed (T) and Relaxed (R) state.
What happens to the hemoglobin during deoxygenation?
A histidine residue on the beta subunit fits between a threonine and proline residue inside an alpha subunit.
What happens to the hemoglobin during oxygenation?
A histidine residue on the beta subunit fits between two threonine residues inside an alpha subunit. This results in a change of shape.
When is the central cavity largest in hemoglobin? (T or R)
T state
When is oxygen affinity highest in hemoglobin? (T or R)
R state
