Biochemistry 6/e

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Transcript Biochemistry 6/e

Sixth Edition
Berg • Tymoczko • Stryer
Chapter 7:
Portrait of a Protein in Action
Copyright © 2007 by W. H. Freeman and Company
(Red cells)
Hemoglobin and Myoglobin
• These are conjugated proteins. A simple
protein has only a polypeptide chain. A
conjugated protein has a non-protein part in
addition to a polypeptide component. Both
myoglobin and hemoglobin contain heme.
• Myoglobin 17000 daltons (monomeric)
153 amino acids
• Hemoglobin - 64500 daltons ( tetrameric)
a-chain has 141 amino acids
b-chain has 146 amino acids
Hemoglobin O2 carrying capability
• Erythrocytes/ml blood: 5 billion
• Hemoglobin/red cell:
( 5 x 109 )
280 million ( 2.8 x 108 )
• O2 molecules/hemoglobin: 4
• O2 ml blood: (5 x 109)(2.8 x 108)(4) = (5.6 x 1018)
or (5.6 x 1020) molecules of O2/100 ml blood
Myoglobin, monomeric
Aromatic Heme
Iron in Hemoglobin binding O2
Hemoglobin, a2b2 tetramer
O2 binding: Hemoglobin & Myoglobin
P50 = 2 torr
P50 = 26 torr
O2 transport capability, a comparison
Resting state vs exercise
O2 Binding Changes 4o Structure
Decreasing O2 affinity
• Lowers the
affinity of oxygen
for Hemoglobin
2,3-bisphosphoglycerate (2,3-BPG)
The binding pocket for BPG contains 4 His and 2 Lys
Binding of bisphosphoglycerate
Oxygen Affinity of Fetal Red Blood Cells
Fetal red blood cells have a higher oxygen affinity than that of
maternal red blood cells because fetal hemoglobin does not bind
2,3-BPG as well as maternal hemoglobin does
The Bohr Effect
Bohr Effect:
• Lowering the
pH decreases
the affinity of
oxygen for Hb
Loss of O2 from Hemoglobin
• CO2 combines
with NH2 at the
N-terminus of
Carbamate formation
Covalent binding at the N-terminus of each subunit
Sickle Cell due to Glu 6  Val 6