Post on 09-Jan-2017
Porphyrin Heme = Fe + porphyrin ring
Heme
Heme A Heme B Heme C
Mitochondria - cytochrome c oxidase - electron transport
O2
Heme = Fe + porphyrin ring – carry O2
Fe2+ located
Most abundant Hemoglobin and Myoglobin
Mitochondria - cytochrome c - electron transport
Fetal Hemoglobin (2α22γ2)
Human Hemoglobin (2α2 2β2)
Sickle cell Hemoglobin (2α22βS
2) Myoglobin 1 α chain
Carbaminohemoglobin Carboxyhemoglobin Oxyhemoglobin
Porphyrin Ring
Porphyrin are ligand bind metal to form complexes Heterocyclic ring contain Carbon/Nitrogen
Form a chelate with metal
Porphyrin containing metal Fe – heme Hemoglobin and myoglobin contain iron porphyrin
Heme
Hemoglobin - 4 chain - 4 heme (porphyrin) - 4 Fe 2+
Fe 2+
Heme (porphyrin)
Hemoglobin - 2 alpha chain - 144 amino acid - 2 beta chain - 146 amino acid
O2 add to Fe as sixth ligand O2 tilt relative to perpendicular of heme plane
His E7 locate over Fe, force CO to bind to Fe at an angle. Steric hinderance reduce afinity of CO in hemoglobin. O2 bind to Fe at an angle, its binding not affected by presence of His E7.
His (E7)
His (F8)
vs
Myoglobin - 1 chain – 1 heme - 1 Fe2+
- 154 amino acid
Hemoglobin Myoglobin
Fe 2+
Heme (porphyrin)
His (F8)
His (E7)
C≡O
Heme
Hemoglobin - 4 chain - 4 heme - 4 Fe 2+
Fe 2+
Heme (porphyrin)
Hemoglobin - 2 alpha chain - 144 amino acid - 2 beta chain - 146 amino acid
Myoglobin - 1 chain – 1 heme – 1 Fe2+
– 154 amino acid
Hemoglobin Myoglobin
Fe 2+
Heme (porphyrin)
Fe in cytochrome 1 polypeptide chain
Fe 2+
Cytochrome c
Bind O2 reversibly/ weak bond Fe2+ bind to O2 (oxygenated )
Hemoglobin + O2 = Oxyhemoglobin
Binding O2 is cooperative binding ↓
Conformational shift caused by binding of O2 at one heme ↓
Makes other heme more receptive More O2 bound to hemoglobin
↓ All 4 binding sites are saturated
% Hb saturation with O2 sigmoidal "S-shaped"curve
Oxygen dissociation curve (ODC)
P50 = partial pressure when hemoglobin 50% saturated O2.
cooperative binding
Hb load/unload O2 reversibly
Hemoglobin
% Hb saturation with O2 sigmoidal "S-shaped"curve
Oxygen dissociation curve (ODC)
P50 = partial pressure when hemoglobin 50% saturated O2.
Factor influence Hb affinity O2
Hb + 4O2 ↔ Hb (O2)4
Shift to right – reduced affinity
↑ Increase temp ↑ Increase pCO2
↓ Decrease pH
Shift to left – increase affinity ↓ Decrease temp ↓Decrease pCO2
↑ Increase pH
cooperative binding
At lung at high O2 conc
% saturation Hb increase
Tissue/muscle at low O2 conc
% saturation Hb drop unloading O2 to tissue
% saturation Hb
pO2
O2 released to tissue
% saturation Hb
pO2
At tissue at high CO2 conc
Shift to right – less affinity % saturation Hb decrease
CO2 ↑
5
98%
48%
50%
pO2 5kPa
48%
88%
At normal % saturation Hb
40% O2 released/unload
to tissue
Hemoglobin
Oxygen dissociation curve (ODC) Factor influence Hb affinity O2
Shift to right – reduced affinity
↑ Increase temp ↑ Increase pCO2
↓ Decrease pH
Shift to left – increase affinity ↓ Decrease temp ↓Decrease pCO2
↑ Increase pH
% saturation Hb
pO2
sigmoidal cooperative
binding
hyperbolic
Myoglobin/Foetal ↓
Shift to left ↓
Higher affinity
Cytochrome responsible for ATP production In electron transport (redox rxn)
Heme conjugated ring system (elec mobile) Iron in form of Fe2+/Fe3+
Heme in cytochrome undergo reversible elec transfer Fe3+ (oxidized) ↔ Fe2+ (reduced)
Foetal/Hemoglobin/Myoglobin
Cytochrome c
Fe in cytochrome in Fe2+/3+
1 polypeptide chain
Fe 2+
Heme = Fe + porphyrin ring
Hemoglobin Fe + porphyrin ring
Chlorophyll Photosynthetic pigment Mg + porphyrin ring
Hemoglobin vs Chlorophyll