Hemoglobin Flashcards
Porphyrin
Four ring structure, has four pyrroles, iron containing porphyrin is the heme.
Prosthetic group
example Heme,
covalently binds to enzyme (hemoglobin)
Ferrous vs ferric
2+ vs 3+
reduced vs oxidized
functional ferrohemoglobin vs nonfunctional methemoglobin
u-oxo bridged dimer
Heme alone will form these dimers as a result of oxidation. Heme is hydrophobic (sticky) so they will clump together.
Hemoglobin and myoglobin feature a hydrophobic pocket which when heme is covalently bound, is protected from oxidation (rust)
Myoglobin vs Hemoglobin oxygen transport ability
Myoglobin has very high affinity for oxygen and is hyperbolic. P50 around 0, that means it only releases oxygen when near hypoxia. It is a last resort to get a blast of oxygen.
Hemoglobin p50 of around 26 Torr, is sigmoidal. P26 is around physiological oxygen concentration and this allows a larger range for delivery. At lowerING Oxygen concentrations, hemoglobin rapidly releases oxygen
Pulse oxometry
oxygenated hemoglobin and deoxygenated hemoglobin absorb light differently depending on the wavelength. Oxygenated and hemoglobin will show the largest difference in absorption at wavelengths 660 and 940
Wear it on your finger and it is used to evaluate oxygen saturation
Hemoglobin
a tetrameric protein with two alpha and two beta globin subunits. One heme prosthetic group is located in the hydrophobic pocket in each subunit so total - 4 hemes, 4 oxygen binding sites.
Subunits are held together by salt bridges
Cooperativity
Is responsible for hemoglobin oxygen saturation’s sigmoidal curve. Its the reliance of multiple parts on each other.
A change in shape of one subunit propagates the change throughout the complex. The first heme needs luck that a subunit will land when it is in the R state, then overcome the binding energy. After that, the structure of the remaining ones change this they can bind easier to oxygen
Hill coefficient
measures the degree of cooperativity.
For hemoglobin/myoglobin
n = 1 always means independence
n = 4 would be for hemoglobin and means perfect all or nothing cooperativity
n = 2.8, somewhere in between realistic to hemoglobin.
Allostery (how is it different from noncompetitive inhibitor?)
Allosteric proteins are always oligomers (multiple subunits) - effectors will bind to site that are spatially distinct from ligand binding sites.
R state vs T state
relaxed vs tense,
oxidized vs deoxidized
Bohr effect - mechanism too
acidification of blood leads to lower affinity of Hb for blood (higher p50).
Why?
The beta chains exhibit Asp 94 and His 146. When pH is low, histidine is protonated and its pKa goes up because it is acting like a base. A salt bridge forms with the negative aspartate. Favors the T state, oxygen is delivered.
When oxygen binds, it forces the molecule to the R state, breaking the salt bridge, so histidine is like fuck it, a proton is released but the local acidification is insignificant.
CO2 affecting binding affinity
mechanism one - CO2 into the blood forms carbonic acid which acidifies the blood, lowering hemoglobin binding affinity - in the lungs hemoglobin releases a proton that reforms carbonic acid and CO2 is then liberated
for other parts of the body, the T state exposes free amines that the CO2 can bind to and stabilizes the T state. (amino terminus of exposed valine)
Diamox (treatment for altitude sickness)
-excretion of bicarbonate (acidifying of blood), this pushes the curve to the right, lowered affinity for oxygen increasing oxygen delivery.
Nitric oxide binding.
NO binds at the R state, directly to a cysteine on the iron of heme. NO is released with deoxygenation and it’ll bind to vascular endothelial receptors, causing vasodilation and increased blood flow.
Nitric oxide delivery depends on the differing reactivity of the R and T forms. NO has a high affinity for Cys 93 in the R from.
