Hemoglobin

Question 1

What is the primary function of Myoglobin(Mb)?

Answer 1

Store oxygen in muscle for release during periods of oxygen deprivation

Question 2

Structural difference between Mb and Hb

Answer 2

Mb has one subunit protein with heme, Hb has 4

Question 3

What is the primary function of Hemoglobin(Hb)?

Answer 3

Carry oxygen gas from lungs to tissues.

Question 4

What is allosteric regulation?

Answer 4

Molecule binding to a region of the protein away from active site.

Question 5

What are the three predominant residues in the interior of Mb?

Answer 5

Phe, Leu, Val

Question 6

What are the four amino acid residues that are on the surface of Mb?

Answer 6

Asp, Glu, Lys, Arg

Question 7

What is the role of the nonpolar residues in Mb?

Answer 7

They protect Fe2+ from oxidizing to Fe3+ as this ion would not bind to O2.

Question 8

Which protein has affinity of O2 dependent on pH, CO2, and 2-3 BPG?

Answer 8

Hb–it has cooperative binding as well

Question 9

What is cooperativity?

Answer 9

Events at one active site of a subunit can influence events at active sites of others.

Question 10

What is a quaternary structure?

Answer 10

Association of two or more protein chains to form a functional unit.

Question 11

MWC vs KNF model of cooperativity

Answer 11

MWC has changes in unison, KNF has changes occur sequentially

Question 12

What state does Deoxy Hb exist in?

Answer 12

Tense state– has a reduced affinity for O2

Question 13

What state does Oxy Hb exist in?

Answer 13

Relaxed state– has a higher affinity for O2

Question 14

What proportion of subunits do 2-3 BPG, pH, and CO2 increase?

Answer 14

T state subunits

Question 15

What would binding of each O2 molecule to Hb due to the equilibria?

Answer 15

It would shift towards the R state more

Question 16

What is the role of Gly25?

Answer 16

Needed for close association of B/E helices

Question 17

What is the role of His92?

Answer 17

Forms coordinate covalent bond with ferrous ion

Question 18

What is the role of Asp94?

Answer 18

Creates salt link with imidazole His146

Question 19

What is the role of Val98?

Answer 19

Carbonyl hydrogen bond with Tyr145/side-chain steric interactions with porphyrin ring

Question 20

What is the role of Tyr145?

Answer 20

OH group forms H-bond with Val98 carbonyl(C=O)

Question 21

What is the role of His146?

Answer 21

Carboxyl group forms a salt link with Lys40 from alpha chain

Question 22

What does the curve of Mb look like

Answer 22

Hyperbolic

Question 23

What does the curve of Hb look like

Answer 23

Sigmoidal

Question 24

What is the affect of 2,3 BPG?

Answer 24

Binds to Hb and reduces its affinity for O2 by stabilizing the Tense state form.

Question 25

What does Deoxy Hb carry and where?

Answer 25

CO2 and H+ from tissues into lungs

Question 26

What does binding to oxygen release?

Answer 26

CO2 and H+ in the lungs

Question 27

Lowering the pH would mean what in terms of affinity?

Answer 27

Lowering pH = more H+, decreases O2 affinity for Hb

Question 28

Increasing the [CO2] would mean what in terms of affinity?

Answer 28

Decreases O2 affinity for Hb

Question 29

What happens if [CO2] is increasing and pH is falling in the tissue?

Answer 29

Hb releases more O2(Bohr effect)

Question 30

Why does lower pH affect the affinity?

Answer 30

Easier protonation of the His146 imidazole side chain, leading to an easier “R” to “T” transition

Question 31

What happens when the His146-ASp94 interaction is compromised?

Answer 31

Loss of ionic interaction leading to a conformational change from T to R state in lungs-> Favors O2 binding. (Heme is pulled back into plane)

Question 32

What is the E6V disease?

Answer 32

Sickle cell anemia. Point mutation occurs where Glu6 is replaced by Valine.

Question 33

What is the affect of the valine mutation?

Answer 33

This creates a hydrophobic patch on dHb, causing aggregation, which leads to a distorted shape. The molecule shifts from R to T state and makes it more difficult to carry O2.

Question 34

What is one drug design that is being used to combat sickle cell disease?

Answer 34

Voxelotor, which shifts the equilibrium of HbS to R state. It does this by decreasing the polymerization of HbS and blunting the effect of 2,3 BPG.