- Tetramer of myoglobin-like polypeptides (dimer of alpha beta subunits)
- Delivers oxygen to tissues throughout the body.
- Once oxygen binds, structural change causes oxygen binding affinity to grow in the three other binding sites
- Hemoglobin has two conformation states:
  - T-state
  - R-state


Hemoglobin

- At low oxygen levels, little oxygen is binding to myoglobin so the YO2 is low.
    - YO2 is the level of saturation of the myoglobin.
- With more oxygen in the system, more oxygen binds to the myoglobin.
- It levels off all oxygen binding sites are filled and myoglobin becomes saturated. 


Oxygen-binding curve of myoglobin

- The first protein with structure determined by X-ray crystallography 
- Smaller protein with oxygen binding behavior 
- Contains the heme group 
- Facilitates oxygen diffusion in muscles by increasing its solubility in muscle cells.


Grand Valley State University

X-ray crystallography is a technique to visualize proteins. This technique utilizes a crystal  of the desired molecule that is exposed to an X-ray beam which then displays a diffraction pattern of the atoms in the molecule. These diffractions are used to to make the 3D image of the protein. 

Drawbacks:
- X-ray only interacts with electrons not the nuclei - the amino acid chains is added to complete the picture
- Lower resolution - possible inaccuracy of the images. 

X-ray Crystallography

Voet, D., Voet, J. G., & Pratt, C. W. (2013). Chapter 7: Protein Function: Myoglobin and Hemoglobin, Muscle Contractions, and Antibodies. In Fundamentals of biochemistry: Life at the molecular level (4th ed., pp. 176-216). Hoboken, NJ: Wiley. Retrieved February 21, 2021, from archive.org.

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