2. Structure of myoglobin
Andrew Kendrew and Max Perutz solved the structure of myoglobin in
1959 to 1968.
Myoglobin was the first protein whose structure was determined by X-
ray crystallography
Myoglobin: 44 x 44 x 25 Å single subunit 153 amino acid residues
121 residues are in an a helix. Helices are named A, B, C, …F. The
heme pocket is surrounded by E and F but not B, C, G, also H is near the
heme.
Amino acids are identified by the helix and position in the helix or by the
absolute numbering of the residue.
11. The Heme group
•Each subunit of hemoglobin or
myoglobin contains a heme.
•Binds one molecule of oxygen
•Protoporphyrin 9
The iron must be in the Fe(II) form or
reduced form. (ferrous oxidation) state.
12. The Conformation
Change The secret of Mb
Oxygen binding changes the Mb
conformation
Without oxygen bound, Fe is out of heme
plane
Oxygen binding pulls the Fe into the heme
plane
Fe pulls its His F8 ligand along with it
The F helix moves when oxygen binds
Total movement of Fe is 0.029 nm - 0.29 A
13.
14. Function of the globin
Protoporphyrin binds oxygen to the
sixth ligand of Fe(II) out of the
plane of the heme. The fifth ligand
is a Histidine, F8 on the side across
the heme plane.
His F8 binds to the proximal side
and the oxygen binds to the distal
side.
The heme alone interacts with
oxygen such that the Fe(II) becomes
oxidized to Fe(III) and no longer
16. MyoglobinMyoglobin
oxygen storage protein of skeletal muscles.
As with the cytochrome example, both proteins use
heme groups. It acts as the binding site for molecular
oxygen.
17.
18. Myoglobin facilitates rapidly
respiring muscle tissue
The rate of O2 diffusion from capillaries
to tissue is slow because of the
solubility of oxygen.
Myoglobin increases the solubility of
oxygen.
Myoglobin facilitates oxygen diffusion.
Oxygen storage is also a function
because Myoglobin concentrations are
10-fold greater in whales and seals than
in land mammals
19. Myoglobin follows the michaelis- menten graph
It follow michaelis-menton because it is a
simple chemical equilibrium
19
24. Myoglobin Structure
Mb is a monomeric heme protein
Mb polypeptide "cradles" the heme
group
Fe in Mb is Fe2+
- ferrous iron - the form
that binds oxygen
Oxidation of Fe yields 3+ charge - ferric
iron -metmyoglobin does not bind
oxygen
Oxygen binds as the sixth ligand to Fe
25. Myoglobin an iron containing protein in muscles
,receive oxygen from rbc and transports it to the
mitochondria of muscle cells,where oxygen is used in
cellular respiration to produce energy
Oxymyoglobin –oxygen supply and act as scavenger of
NO[MYOCYTES]
Oxymyoglobin +NO= Harmless nitrates with ferric
myoglobin ,which is recycled by metmyoglobin
reductase
25
26.
27.
28. O2 binding to myoglobin
22 MbOOMb ↔+
][MbO
][Mb][O
Kd
2
2
=
][OKd
][O
][MbO[Mb]
][MbO
Y
2
2
2
2
O2
+
=
+
=
Written backwards
we can get the
dissociation
constant
Fractional Saturation solve for [MbO2]
and plug in
29. How do you measure the
concentration of oxygen?
Use the partial pressure of O2 or O2
tension = pO2
2d
2
O
pOK
pO
Y 2
+
=
P50 = the partial
oxygen pressure
when YO2 = 0.50
250
2
O
pOP
pO
Y 2
+
=
30. P50 value for myoglobin is 2.8 torr
or
1 torr = 1 mm Hg = 0.133 kPa
760 torr = 1 atm of pressure
Mb gives up little O2 over normal
physiological range of oxygen concentrations
in the tissue
i.e. 100 torr in arterial blood
30 torr in venous blood
YO2 = 0.97 to YO2 = 0.91
31.
32. Contrast Mb O2 binding to
Hemoglobin
YO2 = 0.95 at 100 torr
but
0.55 at 30 torr
a ∆YO2 of 0.40
Hb gives up O2 easier than Mb and the
binding is Cooperative!!
