Hemoglobin and Myoglobin

Question 1

1) Myoglobin:
- Where is it mainly found?
- What is a heme made of, what type of binding does it have/not have?
- what are the 2 important residues that are connected to the heme and what is their function?
- what is the affinity for O2 binding and why is it so different from hemoglobin? What happens to iron when O2 binds to it?

Answer 1

• muscle tissue, storing oxygen
• heme is made of 4 pyrrole rings and and iron group in the middle.
• distal histidine, doesn’t actually bind to Fe, it stabilizes the superoxide group made when oxygen binds to it via H-bonding, Proximal histidine binds to the Fe and pulls down on it to keep it slightly out of the plane in the lack of oxygen. In the presence of oxygen the Fe group shrinks and fits into the plane. Myoglobin has a very high affinity to bind to oxygen but doesn’t release it quickly either.

Question 2

2) Describe the structure of hemoglobin, the names of the helices and the number of hemes each has.

Answer 2

• 2 alpha and 2 beta helices and 4 hemes

Question 3

3) Oxygen binding of myoglobin and hemoglobin:
- what is the myoglobin curve called? Why is it’s affinity higher?
- What is the hemoglobin curve called? What causes this?
- What does fractional saturation Y mean (what is 0 and 1?)
-

Answer 3

• myo curve called hyperbolic, indicates a single binding site, which is why the affinity is higher
• hemo called a sigmoidal curve due to 2,3-BPG, causing cooperative binding, meaning, when the first oxygen bind, the rest bind at a faster rate
• 0 means not oxygen bound, 1 means its full

Question 4

What are the two states of hemoglobin called and what causes these states?

Answer 4

Tense state, deoxy, stabilized in the lack of O2 due to several ion pairs and relaxed state has higher affinity for O2 binding and more O2 binding to it makes it more stable (it breaks the ion pairs).

Question 5

What is an allosteric inhibitor for hemoglobin and what exactly does it do? How exactly does it regulate? What would occur if we lacked it?

Answer 5

2,3-BPG, if reduces the affinity for T state hemoglobin to bind to oxygen. 2,3-BPG has a large negative charge and binds to a + charge portion of the hemoglobin, only in the deoxy state.
When 2,3-BPG lacks, hemo is almost completely saturated in tissues, but in it’s presence it is only 1/3 saturated so it allows O2 to be released.

Question 6

What is different in gamma chain fetal hemoglobin than adult hemoglobin?

Answer 6

It has a lower affinity for 2,3-BPG so it has a much higher affinity for oxygen.

Question 7

In addition to 2,3-BPG, what are some other allosteric modulators of hemoglobin? Explain how each effect the affinity for oxygen binding.

Answer 7

H+ , stabilizes the T state even more by protonating the His group
CO2: carbonic anhydrase reduces the pH, some form carbamates which make the T-state more stable and induce the release of oxygen.

Question 8

Describe what sickle cell anemia is and how it may occur.

Answer 8

Causes anemia, a Glu change to Val, less soluble in deoxy form and forms precipitate, causes blood clots

Question 9

Differentiate between Alpha and Beta thalassemia.

Why doesn’t alpha hemoglobin precipitate during regular synthesis?

Answer 9

Alpha:
- Loss of an alpha chain
- Less common because here are 4 alleles for it
- Causes higher affinity to bind to oxygen, no cooperativity
Beta:
- Anemia
- More common because we have 2 alleles for it
- Causes the alpha chains that are left to form aggregates.
2) stabilizer protein called AHSP