Hemoglobin 3 Flashcards
Contrast the taut state and relaxed state of hemoglobin
Taut state-when fractional saturation is low and no oxygen is bound, the hemoglobin is held together by ionic bonds
Relaxed state- saturated with oxygen, conformational changes break hydrogen bonds ionic bonds to be broken to increase affinity to grab oxygen
What is cooperative ligand binding?
Binding of one oxygen molecule promotes the binding of another oxygen molecule
Why can we say an oxygen molecule is a positive allosteric regulator?
Because binding of a oxygen molecule at one site increases affinity at another site
What is the Bohr effect?
The O2 dissociation curve shifts to the right with decrease in pH (recall that increased PCO2 leads to decreased pH)
How does pH affect oxygen affinity in hemoglobin?
As pH decreases, a higher pO2 is needed to bind the oxygen molecule/ reduced of oxygen for hemoglobin/ rightward shift in oxygen saturation curve
Evaluate the shape of myoglobin dissociation curve and their functions
Myoglobin has a higher affinity for oxygen binding as it delivers oxygen to muscles
Hemoglobin may release oxygen (hence lower affinity and rightward shift on graph) which binds to myoglobin and can deliver the oxygen to hemoglobin
What is Carbonic anhydrase?
It promotes the formation of carbonic acid from CO2
Explain how Caron anhydrase supports life
The dissolving of CO2 into water is spontaneously fast, but nit fast enough to support life, Carbon anhydrase speeds this up
How does formation of bicarbonate ion cause formation of taut hemoglobin?
- protons form/pH drops when bicarbonate forms
- Protonation of His side chains on Hb, forms positive charges
- This allows for addition of additional salt bridges
- this stabilizes the taut form of Hb
- Promotes O2 delivery to tissues
What happens when carbon dioxide reacts with amino terminus of alpha-chains?
Allows formation of additional salt bridges, and also the release H+ ions to strengthen the Bohr effect
What does CO2 react with the amino terminus to create?
NH2R + CO2 = NHR-CO2- + H+
What forms 2,3 Biphosphoglycerate “
Formed from a side reaction in glycolysis
What is the significance of 2,3 bispohosphoglycerate?
2,3 BPG is a potent regulator of Hb oxygen affinity
Negative charge on OPO3 ^2- slips between aB dimers to form salt bridges with with histidine amino acids (which can be differentially protonated, depending on pH of the solution)
What kind of charge does 2,3 BOG have?
There are negative charges on a very small molecule
Summarize all the functions of 2,3 BOG in hemoglobin
Promotes formation of taut state; decreases O2 affinity for Hb:
- 2,3 BPG allows the formation of additional salt bridges between the two aB dimers
- At the interface between the two aB dimers
- This creates a driving force for Hb to assume the deoxyHb structure(taut form)
- promotes O2 unloading
What kind of allosteric effector is 2,3 BPG? Why?
A negative allosteric effector
It causes a rightward shift and a sigmoidal curve is impossible without 2,3 BPG (hyperbolic)
How do high altitude athletes have a different oxygen affinity?
High altitudes cause lower oxygen affinity of Hb to promote unloading
What are the allosteric effects?
Regulation of O2 delivery by Hb depends on allosteric (“other site”) effectors:
- pO2
- pH of environment
- pCO2 (which influences pH, and taut/relaxed state
- 2,3BPG availability
- temperature increases thermal energy (exercises ) causes a rightward shift and O2 leaves
Myoglobin not regulated this way
Where should O2 affinity be high?
In the lungs to promote binding to Hb
Where should O2 affinity be low?
In tissues where they need to be released
Summarize the actions in the lung that affect oxygen affinity as CO2 is released
- CO2 and 2,3 BPG are pushed out
- As CO2 is exhaled, pH goes up
- Protons come off His amino acid
Summarize the actions that affect Oxygen affinity as O2 binds to hemoglobin
- High partial pressure of O2 forces itself onto ?Hb
- As the animal exhales, CO leaves the body, raising the pH
- Saturated O2 forces 2,3 BPG off of Hb
- As 2,3 BPG comes off of Hb, protons must leave as well( as they lose their negative charge partner)
What drives O2 loading in lungs?
High partial pressure of O2 drives the loading of O2 in the lungs
Why is CO2 thought to be a volatile acid?
It can leave the body as a gas
How does CO2 leave/exhaled through the lungs?
- Carbonic acid decomposes to form CO2 which is exhaled, to raise the pH
- Also, CO2 bound to N-terminal end of the alpha-globin subunits is released
What promotes offloading in tissues?
Low pO2, lower pH and the presence of 2,3 BPG
Contrast CO binding with O2 binding
- CO reversible binds to the Fe2+ the same way that O2 does
- In free heme, (no protein), CO binds 20,000-25,000
- free heme binds preferably to CO 25,000X more tightly than O2
Contrast CO binding with feee heme with homoglobin
When in the hemoglobin protein, the affinity of Hb for CO is reduced to approximately 200-250x the affinity for O2
In heme- CO binds 20,000-25,000
How does CO bind to Hb?
- Hb forces CO to bond at an angle
- Reduces the CO to Fe bond strength
- Now it is only about 200x stronger than oxygen
- CO binding to Hb is stronger than O2 binding, but is now reversible(we would die otherwise)
What type of hemoglobin is carboxy hemoglobin HbCO?
CO + Hb= HbCO
How does CO binding affect O2 binding?
- CO causes a relaxed Hb strongly, preventing 2,3 BPG from entering
- causes holding onto too O2 tightly preventing O2 from leaving
How much HbCO is fatal?
50 to 60%
How can high HbCO be treated?
- O2 therapy( 100% oxygen)
- higher pressure
- hyperbaric medicine
Describe the structure-function of fetal hemoglobin
- Has a few less histidine amino acids at the dimer interface
- Causes less binding affinity for 2,3 BPG
- so fetal hemoglobin has a stronger oxygen affinity
