Hemoglobin Molecule - Structure & Function
Myoglobin Structure and Function
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Myoglobin (Mb) is a structurally complex molecule that binds and stores oxygen inside of skeletal and cardiac muscle cells.
- A large, coiled polypeptide called
globin makes up most of the molecule.
- In a hydrophobic pocket formed by two of the globin’s folds is a heme group. The heme consists of an atom of ferrous iron (Fe2+) and a surrounding porphyrin ring (= four nitrogen-containing pyrrole molecules.
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- The iron can reversibly bond with one molecule of oxygen (O2).
- Two histidine molecules are associated with the heme. On one of the sides of the heme is the proximal histidine, which binds the Fe2+ of the heme to the nearby globin. It helps stabilize the position of the attached heme.
- The distal histidine, which is not bound to the heme, helps prevent oxidation of Fe2+ to Fe3+. Oxygen does not bind to Fe3+.
- The distal heme also reduces carbon monoxide’s (CO) affinity for heme, which makes it easier for O2 to bond.
An Overview of the Myoglobin Structure and Function:
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The changes in blood plasma pH, CO and CO2 affect the oxygen-hemoglobin saturation.
Oxygen Myoglobin Dissociation Curve
If an isolated muscle fiber has been placed in a vial of deoxygenated blood. Inside the muscle fiber, each molecule of myoglobin can bind one O2. The O2-Mb bond is reversible, and the direction of the reaction is dependent on the concentration of O2 (partial pressure or pO2) in the surrounding fluids.
Hemoglobin Molecule – Structure & Function
Hemoglobin structure in a detailed, interactive and illustrated tutorial (globin, alpha and beta subunits, porphyrin, heme groups,…etc) with colorful and simple animations about its states (relaxed & tensed).
