1. 生化重點整理
第9組
B983B0045 許憲文
B983B0022 杜碩恩

2. 心智圖 4 in the plane monomeric 6 ligands His F8 Heme myoglobin Fe2+ O2
features
O2 affinity ( His E7 )
tetrameric
2 α chains
Part3.
The example of allostery
Hemoglobin
structure
2 β chains
features
O2 affinity ( by ρO2 ) O2
protons
enzyme
The Bohr effect (Hb)
Carbon dioxide
carbamate
Chloride ions
β chain
BPG
(2,3- bisphosphoglycerate)
Loss of O2

3. 重點整理 A classic example of allostery: Myoglobin & Hemoglobin.
Bohr effect: saturation curve of Hb for O2 is displaced to the right as acidity increases.
Myoglobin
Hemoglobin
Structure
Monomeric
Tetrameric(2α chains 2β chains)*
Affinity for O2
Great
Normal
Oxygen released
pO2 ~40 torr
pO2 less 20 torr
O2 binding curves
Classical Michaelis-Menten-type
Sigmoid-shaped
*Fetal hemoglobin exists as an α2γ2 tetramer (decreased BPG binding, higher affinity for oxygen than maternal).

4. Myoglobin & Hemoglobin.
Myoglobin: ferrous iron (Fe2+) is form that binds oxygen. Mb polypeptide protects the heme iron atom from oxidation. His E7 force the CO to tilt away (25000X→250X).
Hemoglobin: deoxy Hb (T form) is stabilized by specific hydrogen bonds and 8 salt bridges. CO2 is directly transported by Hb in the form of carbamate (—NHCOO-).

5. Myoglobin Ferrous iron (Fe2+) is form that binds oxygen.
Mb polypeptide protects the heme iron atom from oxidation.
His E7 force the CO to tilt away (25000X→250X).

6. Hemoglobin
Deoxy Hb (T form) is stabilized by specific hydrogen bonds and 8 salt bridges.
CO2 is directly transported by Hb in the form of carbamate (—NHCOO-).
The binding of 2,3 – bisphosphoglycerate (2,3-BPG) to Hb promotes the release of O2.
Sickle-cell anemia: one amino acid exchange, Hb S molecules aggregate into long, chainlike polymeric structures.

7. 習題 Why are we protected to some extent against low level CO poisoning?
Ans：His E7 blocks perpendicular binding of CO to heme iron allowing for better binding competition by O2.
What are characteristics of myoglobin's peptides?
Ans：candles the heme group
protects the heme iron atom from oxidation
provides a pocket into which the O2 can fit