Proteins: Myoglobin & Hemoglobin (Chapter 6)

Question 1

What does Heme consist off?

Answer 1

4 pyroles linked via Methyne bridges.

Question 2

What do we find inside heme?

Answer 2

Fe2+

Question 3

What happens if there is oxidation of Fe2+/Fe3+?

Answer 3

it destroys the biological activity of myoglobin and hemoglobin.

Question 4

discuss myoglobins structure

Answer 4

Consists of 8 Right handed Helices.
On the surface we have polar AA
on the interior we have Non-polar AA apart from two (His E7, HisF8)

Question 5

Discuss HisE7 and HisF8 and the iron ion

Answer 5

Heme lies between the helices E and F.

Iron is bound on it’s 5 co-ordination position by the nitrogen in the imidiazole ring of Histidine F8.

Question 6

What happens in terms of movement of Amino Acids when oxygen binds to fe2+?

Answer 6

Initially fe2+ lies 0.03nm outside of the ring.
when oxygen binds to it, it pulls it towards the ring, which causes movement of His F8 which causes movement of the amino acids connected to it.

Question 7

What subunits make up haemoglobin off:

1) Adult
2) Fetal
3) Sickle cell

Answer 7

1) a2b2
2) a2y2
3) a2 b(s)2

Question 8

What is co-operative binding?

advantage of co-operative binding?

Answer 8

When one molecule of Oxygen binds to Haemoglobin, the other readily binds to it with higher affinity.

Advantage:
Allows oxygen to bind at p(o2) of lungs
and deloads at tissue.

Question 9

What does P50 show?

What does comparison of p50 of fetal and adult haemoglobin show.

Answer 9

P50 shows the p(O2) of which the heme is half saturated.

Fetal p(o2) = 20
adult p(o2) = 26
Lower p(o2) means higher affinity to oxygen.

Question 10

When does synthesis of b subunit in haemoglobin begin?

Answer 10

Begins in 3rd trimester.

Question 11

How does oxygenation explain conformational change?

Answer 11

• Binding of oxygen causes shifting of iron towards plane of heme.
• This pulls His F8 which pulls the other residues.
• This ruptures salt bridges so Hemoglobin is in R-state.

Question 12

1) What is carbamation?

2) How does Carbamation affect the state of haemoglobin?

Answer 12

1)Method of Hemoglobin carrying co2.
Co2 + Hb-NH3+ —> Hb-NH-COO + 2H+
Carbamate forms with terminal amino

2)Carabamate formation causes changing from positive to negative charge, which favours salt bridge formation so T-form.

Question 13

Equation for formation of Bicarbonate Ion

Answer 13

Co2 + H20 H2Co3 —–> HCO3- + H+

first step catalysed by carbonic anhydrides.

Question 14

1) How many protons does deoxyhaemoglobin bind for every oxygen released?
2) Important of deoxyhaemoglobin binding to protons?

Answer 14

1) proton for every 2 oxygen released.

2) Buffer effect

Question 15

What stabilises the T-state?

Answer 15

• carbamation
• Low pH
• 2-3BPG

Question 16

What is the Bohr effect?

Answer 16

• Deoxyhemoglobin binds to protons.
• takes them to the lungs.
• released for O2.
• The proton combines with bicarbonate ion to form acid, this then released as co2.

Question 17

How do protons arise?

Answer 17

arise when there is rupturing of salt bridges..

Question 18

When is 2-3 BPG formed?

and where does it bind?

Answer 18

2-3 BPG is formed when there is low p02 in the tissues.

In T-state it binds btw the H-Helices of the B subunits.

Question 19

What is the effect of BPG?

How does it cause this?

Answer 19

BPG stabilises the T-state.
It does this by forming salt bridges to terminal amino via:
-Val
-His
-Lys

Question 20

How does 2-3BPG’s effect differ in fetus?

Answer 20

It binds weakly compared to in Adults.
Instead of His, it binds via Ser.
This explains why Fetal Hemoglobin has higher affinity than Adult.

Question 21

1) What is Methomoglobin?

2) What causes this?

Answer 21

1)Fe3+ instead of F2+
So cannot bind to O2.
2)-Sulfonamides
   -Hereditary
   - Reduced activity of methemoglobin (which reduces f3+ to fe2+)

Question 22

What do we find in Haemoglobin M?

Answer 22

His F8 has been replaced for Tyrosine.

Question 23

What do we find in Sickle Cell Anemia?

Answer 23

Valine has been replaced for Glu6

This generates a hydrophobic sticky patch.

Question 24

What is Myoglobinuria?

Answer 24

Following a massive crush injury to skeletal muscle.

Myoglobin may be found in urine.

Question 25

How can we detect myoglobin in the Urine?

Answer 25

-Assay of serum enzymes.