Hemoglobin

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(Raven, 2012)

BIOCHEMISTRY: Protein Function–Myoglobin and Hemoglobin by A. Scheider 1
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Alpha helix polypeptide chains

Heme complex with Oxygen attached to iron Heme complex without Oxygen attached to iron

Beta sheet polypeptide chains

Model of Hemoglobin Molecule
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Hemoglobin: quick facts
Hemoglobin is a protein that carries Oxygen and releases Oxygen to the body via the blood circulation. Hemoglobin is made of 4 polypeptide chains with each chain containing an iron-heme structure that contains the oxygen-binding site. Each hemoglobin molecule twists a polypeptide chain into a helical secondary structure. The helices drape around the heme group and form into a tertiary structure subunit. The four subunits are packed into a globular quaternary protein structure. The iron-heme structures give the red color to hemoglobin. Each hemoglobin molecule can carry and/or release a maximum of 4 oxygen molecules. The oxygen is picked up in the lungs and delivered to tissues as neede.d

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Oxygenated and Deoxygenated states of Hemoglobin (Hgb)
A molecule of hemoglobin loaded with oxygen is referred to as oxyhemoglobin. Oxyhemoglobin is an unstable protein that easily reverses its’ oxygen attachments. When a molecule of hemoglobin is empty of oxygen attachments, it is called deoxyhemoglobin. Portions of the terminal end of the amino acids in the deoxyhemoglobin will work together to form ionic pairs. Tuesday, March 12, 13

These ionic pairs decrease the acidity of the blood by binding one hydrogen atom for every 2 oxygen molecules released. The resulting lowering of blood pH will trigger the intake of more oxygen. Deoxyhemoglobin presents in a bluish red color in the blood while oxyhemoglobin is bright red.

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(Childs, 2012)

Myoglobin vs Hemoglobin
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Heme= Fe-protoporphyrin IX C34H32FeN4O4
Both Myoglobin and Hemoglobin contain the HEME complex which enables Oxygen to attach and release to ferrous iron. Heme is responsible for red color of blood and muscle. (Prahl, 1998)

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Myoglobin Structure
Oxygen binds to heme in both hemoglobin and myoglobin. Myoglobin is a single polypeptide chain. Contains one iron (Fe 2) protoporphyrin/heme group. Arranges 153 amino acid residues in 8 helical areas (A-H) with heme structure containing single iron atom (Fe 2), Stronger bonding to oxygen than Hgb. Stored and used in muscle tissue.

Myoglobin protein
HIS

------heme complex
Distal histidine = reversible oxygen attachment

HIS

Heme complex containing Fe 2

(Sugimoto et al, 2007)

Proximal Histidine holds heme in place

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Hemoglobin Structure
Hemoglobin (Hgb) is carried by the blood and is made of 4 subunits of polypeptide amino acid chains. Each chain has a similar structure to myoglobin protein. Hemoglobin Protein Globule
HIS HIS

Hemoglobin can carry up to 4 oxygen molecules as there are 4 polypeptide chains each with a heme complex.

2 - 72 amino acid alpha chains subunits.

Like myoglobin, amino acid chain contain the heme complex. Heme complex is associated with oxygen binding and is held in place by interaction between the iron atom and nitrogen atom from histidine side chain. Unlike myoglobin, Hgb gives up O2 easily.

2 - 73 beta amino acid chains subunits.
HIS HIS

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Bohr Effect
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Hgb Saturation

Tissue

Lungs

Oxygen Partial Pressure
("Bohr effect," 2012)

Hemaglobin (Hgb) Saturation Curve The “Bohr Shift”
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When the metabolic needs of tissues increase as during exercise or stress, the hemoglobin molecule will release more of its oxygen molecules than during lower metabolic needs. Both carbon dioxide (CO2) and Hydrogen (H) increase during increased metabolic activity in the body. As more CO2 is made during exercise, it reacts with...
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