Structure and Function of Hemoglobin and Myoglobin

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Structure and Function of Hemoglobin and Myoglobin

• Chemistry II
• Mrs Baker

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Introduction - Globular Proteins

• Globular proteins have no systematic structures
  but most contain substantial amounts of ?-helices
  and ?-sheets.
• Relatively spherical in shape.
• Include egg albumin, hemoglobin, myoglobin,
  insulin, and many enzymes.

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Hemoglobin

• Consists of 4 polypeptide chains - tetramer
• 2 ? chains
• 2 ? chains
• ? and ? refer to the types of polypeptide chains
  - helical secondary structures with no ? sheets.
• Folds to form a globular tertiery structure.
• The 4 subunits form a quaternary structure.
• Each of the 4 folded helices form a pocket that
  holds a heme group.
• Transports oxygen in the red blood cells to
  tissue cells.

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Myoglobin

• Consists of a single, helical polypeptide chain.
• Folds to form a globular structure.
• Holds 1 heme group.
• The heme group stores oxygen in the muscle cells.

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Structures

• Hemoglobin Myoglobin

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Heme

• Made of a series of nitrogen 5 member cyclic
  rings that are further joined to each other by
  more rings.
• At the center is Fe2.
• Fe2 coordinates with 4 nitrogens, each of which
  contribute 2 electrons, forming coordinate
  covalent bonds.
• O2 coordinates with the Fe2 as well.

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Heme
http//en.wikipedia.org/wiki/Heme
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Heme carrying O2
O2
His F8
http//chemed.chem.purdue.edu/genchem/topicreview/
bp/1biochem/blood3.html
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Heme carrying O2

• Fe2 has 6 coordination sites.
• 4 are occupied by the nitrogens.
• The 5th coordination bond is with a nitrogen atom
  from a histidine side chain on an amino acid in
  the protein (His F8).
• The last site is occupied by O2.
• Hydrophobic interactions between the heme and
  hydrophobic amino acid R groups in the protein
  stabilize the heme protein conjugate.

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Myoglobin/Hemoglobin

• Myoglobin serves as the intracellular storage
  site for O2 in muscle tissue.
• Strenuous exercise can create periods of oxygen
  deprivation and oxymyoglobin releases its bound
  oxygen for metabolic purposes.
• Myoglobin has a greater affinity for O2 than
  hemoglobin.

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Myoglobin/Hemoglobin

• Hemoglobins ability to release oxygen is
  affected by
• pH
• CO2
• Differences in the lung environment - O2 rich and
  the tissues - O2 deficient.
• How does hemoglobin gain and lose O2?
• Activity