Hemoglobin

Question 1

what are the two conserved amino acids important in both myoglobin and hemoglobin

Answer 1

• proximal Histidine F 8

- distal Histidine E7

Question 2

what are the 6 coordination points for Fe in hemoglobin and myoglobin

Answer 2

4 nitrogens of porphyrin ring
nitrogen of proximal histidine
O2 molecule

Question 3

why is the Mb oxygen disassociation curve hyperbolic?

Answer 3

• Mb monomeric protein binds one molecule of O2 per monomer

- the binding of O2 to one monomer has NO effect on the binding of O2 to another monomer

Question 4

why is the Hb oxygen disassociation curve sigmoidal?

Answer 4

Binding of one O2 increases the chances that the remaining
sites in that tetramer will become occupied.
Exit from one site increases the chance that the remaining
sites in that tetramer will be emptied.

Question 5

describe the steps of O2 binding to Hb and how that contributes to the observed sigmoidal curve of Hb

Answer 5

1. O2 coordinates with the Fe+2 of the porphyrin ring of one globin of the tetramer, and is stabilized
   by interactions with His E7.
2. Fe+2 drops into the plane of the porphyrin ring.
3. His F8 moves to accommodate the ionic diameter of the Fe+2.
4. The above includes a movement of Helix F and additional alterations in 3° and 4° structure of the
   tetramer as a whole.
5. The above includes a 12‐15° rotation of one αβ dimer with respect to the other αβ.

Question 6

Heme:Heme interaction is an example of ___ Cooperativity

Answer 6

positive

Question 7

what is the Hill coefficient? Compare Hb’s hill coefficient to Mb coefficient

Answer 7

Hill coefficient is a mathematical expression of cooperativity. Hb hill coefficient is around 2.7 and Mb’s is 1 (no cooperativity)

Question 8

which form of Hb has more interdimer bonds?

Answer 8

T. the inter-dimer bonds are noncovalent

Question 9

what is homotrophic allosterism?

Answer 9

substrate binding on on a multi-subunit protein. In Hb’s example, its O2

Question 10

what is heterotrophic allosterism? What are the heterotrophic allosteric regulators for Hb?

Answer 10

• non-substrate binding on multi-subunit protein

- H+, CO2, 2,3 BPG

Question 11

what is the Bohr Effect?

Answer 11

This differential binding of O2 to Hb, dependent
upon pH, is referred to as The Bohr effect.
-CO2 as well

Question 12

what chemical effect explains the Bohr effect

Answer 12

The lower pH of metabolically active deep tissues
(7.2) favors protonation, and ionic bond formation.
The higher pH of the lung (7.6) favors deprotonation
and elimination of the ionic bonds. These changes in
pH promote changes in the T / R balance… and in O2
binding.

In other words: as the [H+] increases in transit from
the lungs to metabolically active deep tissues,
protonation of key residues favors formation of the
T‐form of Hb, therefore acting in concert with low
[O2] to promote efficient O2 release and delivery to
those deep tissues.

Question 13

what is 2,3 BPG?

Answer 13

2,3 bisphospho‐glycerate is produced in red blood
cells via a side‐reaction off of glycolysis.

It is a highly negatively charged molecule.

Its synthesis is stimulated by hypoxia… lung
disease,
presence at high altitude, and by consumption of
cigarettes…

Question 14

where does 2,3-BPG bind to Hb

Answer 14

between the two B subunits in a positively charged pocket. Only bound to T form Hb

Question 15

T/F: HbF can bind 2,3-BPG similar to how HbA does?

Answer 15

False, HbF does not bind 2,3-BPG as well

Question 16

what are 3 compounds that Hb transfers

Answer 16

• O2
• CO2
• NO

Question 17

describe the physiological effects of NO

Answer 17

In vascular smooth muscle tissues: It binds to surface receptors, activating an intracellular
guanylate cyclase. Resulting increased cGMP concentrations stimulate a cGMP‐dependent
kinase (protein kinase G) that in turn leads to phosphorylation of contractile apparatus
proteins and relaxation of smooth muscle, followed by dilation of blood vessels…. THEREBY
increasing blood flow and O2 delivery.

Question 18

which form of Hb does NO prefer to ride on

Answer 18

R form.
When Hb converts from R–> T form, it releases O2 and NO. Thus NO increases efficiency of O2 delivery by causing vasodilation

Question 19

whats the physiological effect of sildenafil?

Answer 19

• increases the half life of cGMP
• which thinking of NO, increases the activation of the cGMP dependent protein kinase which leads to phosphorylation of contractile apparatus proteins and relaxation of smooth muscles

Question 20

what congenital issue can lead to MetHb?

Answer 20

via autosomal recessive inheritance of a
defect in the protective enzyme (NADH
methomoglobin reductase, aka cytochrome‐B5
reductase)

Question 21

what problem occurs in MetHb?

Answer 21

Hb binds O2 when its Fe is in the +2 (ferrous state)
only. Oxidation of Fe to the +3 (ferric state) no longer
accommodates O2 binding. H2O binds in its place.

Question 22

what treatment should be given to a patient with MetHb

Answer 22

supplemental O2 and methylene blue

Question 23

what treatment can be given to patients with HbS to reduce painful episodes

Answer 23

Hydroxyurea .It raises the level of HbF and the haemoglobin level.
-HbF seems to “poison” the chain that seems to happen when HbS are on the T state are start to connect via hydrophobic patch