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Hemoglobin and Red Blood Cells
Hemoglobin quaternary structure,
Contains 2a and 2b subunits
At max. capacity, the average human’s
blood cells can hold over a liter of oxygen
Heme in Hemoglobin (Hb) a Myoglobin (Mb)
Heme
Myglobin is a monomeric protein
(only 1 protein) and contains 1 heme.
Heme
Hemoglobin is a tetrameric protein
(4 proteins) and contains 4 hemes.
Deoxyheme and Oxyheme
Fe2+ + O2
Fe2+
(5 ligands bound)
(6 ligands bound)
= True color in
O2 poor blood
= True color in
O2 rich blood
For many years, scientists thought the veins where
blue do to oxygen poor blood. We no longer believe
this is the case, but that there is an optical effect.
Many types of Iron Oxides are red.
Consequently, it is the iron in
blood which cause it to be red.
MRI + Hemoglobin has allowed us to view the
Human Brain in Action
The affect to the left
has been triggered by a
man sensing a smell.
The regions of the
brain consuming O2 are
primarily of the
olfactory cortex which
can be visualized do to
differences in the MRI
between oxy and
deoxy hemoglobin.
Hemoglobin = 2a and 2b subunits
Labeling of a and b subunits:
3D Hemoglobin:
O2 Delivery by Hemoglobin
Hemoglobins ability to delivery 66% of
it O2 to oxygen deprived cells makes it
far superior to Myglobin for O2
delivery.
Your Hemoglobin delivers 45% more
O2 when you exercise then at rest.
Grog the Alien hails from the Planet Weeiirddoo.
Looking at Grogs Hb plot, would you think
Weeiirddoo has more or less O2 than Earth?
Human Hb
Grog Hb
Grog the alien (often mistaken for
old chemistry professors)
More O2 … as it requires more O2 to saturate his Hb
Hemoglobin: Conformation Changes with Binding of O2
Binding of O2 to the a-Subunit of Hemoglobin
In Deoxyhemoglobin,
the iron atom is 0.4
angstroms out of
plane
Once O2 binds, Fe
goes completely in
plane with the heme.
Fe movement pulls
the bound His
upward
completely
shifting an a-helix
2,3-Bisphosphoglycerate Effect on Hemoglobin
The presence of BPG makes
a difference of transferring
8% vs. 66% of the oxygen
BPG binding
pocket
Notice how this
pocket is full of
positively charged
residues like Lys
and His. This
increases
interaction with
negatively charged
BPG.
BPG Binding Site in Embryos
Embryos, have different Hemoglobin that consists of 2a and 2g units. g is really similar
to b, with the exception that at the BPG binding site His 143 is replaced w/Serines.
The result is BPG doesn’t bind as
well and the T-state not as stable.
This allows easy transfer of O2 from
mothers hemoglobin to the babies
hemoglobin.
Carbon Monoxide Poisoning
Due to similar shape, CO binds like O2 to
Hemoglobin:
Why CO is deadly:
1. Binds Fe2+ 1000x stronger than
O2 (out competes sites on Hb)
2. Forces Hb into R-state (BPG can’t
bind and O2 bound can’t be
released well)
3. The result of above is the
suffocation of brain cells that
leads to death
Roughly 2500 people die of CO each year: 2000 are suicides.
Treatment: expose to pure O2
His 146 and Asp 94 in Hemoglobin
- At pH 7.2, about 33% of His 146 is protonated
- At pH 7.4, about 20% of His 146 is protonated
Salt Bridges at
Lower pH promote
the T-state (which
releases O2 to form
deoxyhemoglobin)
Loss of Salt Bridges at
Higher pH promote
the R-state (which
binds O2 to form
oxyhemoglobin)
Transfer of CO2 from Tissue to Lungs
Dissection of Hemoglobin
What
Whatfunction
functiondo
dothe
theoutside
salt bridges
polarperform?
Amino
Stabilize
T-form of
Hb
Acid residues
on thethe
a-helices
perform?
What functions do the lactic acid and CO2
Make hemoglobin water soluble (inside Red
perform?
What function
theCells)
His atoms
attached
to the
functionsdoes
do
the
Iron
perform?
Blood
Bind
Oxygen
in doing
so cause
a small
Iron
atom
The
acidperform?
ofand
lactic
acid and
Carbonic
Acidshift
into
the
plane
of the
Shifts
anisa-helix
which
converts
the whole
(which
formed
from
COporphorin
2), protonate
hemoglobin
a T-stateThe
to more
residues
thatstructure
form the from
salt bridges.
salt
of an R-state
bridges push Hemoglobin
toward a T-state
which promotes the release of O2
What function does BPG perform?
Polar surface map of a-subunit in Hb Binds to a BPG pocket which stabilizes T-state,
All red and blue are charged
BPG pocket collaspes apon binding of 1st O2 to
Hemoglobin
Sickle Cell Anemia
Normal
Red Blood
Cell
Sickle
Red Blood
Cell
Sickle and Hammer in
USSR symbol to indicate
“worker party”
“Sickeled Cells”
can easily clog
blood vessels
Sickeled Cell
Anemia gene
commonly found
in Africa and India
Hemoglobin Sickle (HbS)
S fibers in Red Blood Cells
Under electron microscope
Sickled RBC Formed Upon Release of O2
O2 release
O2 binding
Normal looking RBC
R-state HbS
R-state HbS
Sickled RBC
A person suffering from sickle cell anemia
will contain both “normal” looking red
blood cells and sickled red blood cells.
The “normal” looking cell will contain
more R-state HbS than the sickled cells.
Sickle Cell and Malaria Density Maps
Woolly Mammoth’s Hemoglobin
Hemoglobin from a 43,000 yr old frozen baby woolly Mammoth
extracted: Oldest know hemoglobin
Problem: Hemoglobin does not bind O2 from cold air. Since
Woolly Mammoths lived in the arctic they had to adapt their
hemoglobin to match the environment.
Wooly Mammoth’s Hemoglobin
Key Mutations (only on b chain, a chain contains no mutations):
Thr12 -> Ala12 ; Ala86 -> Ser 86; Glu101 -> Gln 101
Glu 101 -> Gln 101 removes a salt bridge, reducing T-state Hb
formation
Woolly Mammoth’s Normal Hb
Hb near the lungs
Woolly Mammoth’s
Hb near tissue
Results of Mutation:
1. Woolly Hb binds O2
stronger near the lungs (this
compensates for the cold).
2. Woolly Hb is more
effected by changes in acidity
(this compensates for the
higher affinity of Hb for O2)