Lecture 11 - O2 transport and Storage by Haemoglobin and Myoglobin Pt. I

Question 1

What is the primary structure of Myoglobin?

Answer 1

150 amino acids

Question 2

What is the secondary structure of Myoglobin?

Answer 2

8x alpha helices (labelled from A - H) and connecting loops

Question 3

What is the tertiary structure of myoglobin?

Answer 3

globin fold with a hydrophobic pocket

Question 4

What is the quaternary structure of myoglobin?

Answer 4

Monomeric (single polypeptide)

Question 5

Where does the Haem bind to in myoglobin?

Answer 5

HisF8 (8th amino acid in helix F, which is a histidine residue)

Question 6

What is Haem?

Answer 6

a prosthetic group, or cofactor

Question 7

What is the basic structure of Haem?

Answer 7

four pyrrole rings linked together in a plane

Question 8

How many coordinate bonds does iron (Fe) have?

Answer 8

6

Question 9

What does the iron bind to in Haem?

Answer 9

4 binds to Nitrogen atoms in haem, 1 binds to a nitrogen atom of HisF8 in the globin, 1 binds to O2

Question 10

Is the binding of oxygen to Fe2+ in haem reversible?

Answer 10

yes

Question 11

What does a higher concentration of a molecule mean in spectroscopy?

Answer 11

less transmitted light and therefore higher absorbance

Question 12

What does the beer lambert law convert?

Answer 12

absorbance of solution converted to concentration of solution

Question 13

What is the purpose of spectroscopy?

Answer 13

Quantifying dissolved molecules based on the principle that different wavelengths are absorbed more or less efficiently

Question 14

How can you determine if Haem is bound to an oxygen?

Answer 14

Haem has visible absorbance and therefore colour that differs between bright red oxyhaemoglobin (HbO2) and darker red deoxyhaemoglobin (Hb)

Question 15

What else can change the shape of a spectroscopy spectrum?

Answer 15

colour, and nature of solute

Question 16

How many globin subunits make up haemoglobin?

Answer 16

4 (usually 2 alpha, 2 beta)

Question 17

how to the globin proteins in haemoglobin associate together?

Answer 17

non-covalently

Question 18

What is the max number of O2 molecules that haemoglobin can hold at once?

Answer 18

4 (one per haem)

Question 19

What is the common mechanism of Myo/Haemoglobin O2 binding?

Answer 19

1. Haem Fe2+ is attached to globin protein by coordinate linkage to His F8
2. Another His (from helix E) on opposite side of haem distorts binding of gas molecules to 6th coordination position on haem Fe2+
3. This reduces binding affinity of oxygen making it easier to release oxygen to the muscle cell when needed

Question 20

What is the function of myoglobin?

Answer 20

oxygen storage in tissues, needs to hold oxygen until it is required

Question 21

What is the function of haemoglobin?

Answer 21

must acquire O2 from lungs and deliver to tissues, must bind O2 more weakly to release at correct time.

Question 22

What type of curve is myoglobins binding curve?

Answer 22

hyperbolic

Question 23

When is myoglobin saturated with oxygen?

Answer 23

at low partial pressure of oxygen

Question 24

When does myoglobin release O2 to cells?

Answer 24

when cellular partial pressure of oxygen is very low

Question 25

What is the partial pressure (pO2) of oxygen in lungs?

Answer 25

about 100 Torr

Question 26

What is the partial pressure (pO2) of oxygen in resting muscle?

Answer 26

about 20 Torr

Question 27

What type of curve is the binding curve of Haemoglobin?

Answer 27

a sigmoidal curve

Question 28

When does Haemoglobin become saturated?

Answer 28

When there is a very high pO2 (ie in the lungs)

Question 28

When will Haemoglobin give up oxygen?

Answer 28

In the tissues at low pO2 where as myoglobin would typically remain saturated at that pO2

Question 29

What allows the local environment to control the affinity of oxygen for haemoglobin?

Answer 29

Allostery, and CO-operativity

Question 30

What does cooperativity require?

Answer 30

• an oligomer (which is a tetramer in the case of haemoglobin)
• multiple interacting subunits

Question 31

What is allostery?

Answer 31

binding of molecules, regulators or post-translational modifications away from the active site

Question 32

What is the function of allostery?

Answer 32

can help regulate binding

Question 33

Are all allosteric proteins oligomers?

Answer 33

No can be monomers OR oligomers

Question 34

What does the ‘Allo’ mean in allosteric?

Answer 34

something changing away from the active site

Question 35

What represents the co-operative behaviour of Haemoglobin?

Answer 35

Sigmoidal binding curve shows two different states that have different affinities for oxygen

Question 36

What are the two states of haemoglobin?

Answer 36

Tense (T) state, and Relaxed (R) state

Question 37

Does the T-state have high or low O2 affinity?

Answer 37

low

Question 38

Does the R-state have high or low O2 affinity?

Answer 38

high

Question 39

Which proteins are often co-operative?

Answer 39

highly regulated proteins/enzymes

Question 40

When do enzymes diverge from michaelis-menten kinetics?

Answer 40

when they are co-operative

Question 41

What do haemoglobin and myoglobin have in common? (3)

Answer 41

1. O2 binds to iron of haem
2. Shift from dull to bright red allows monitoring O2 binding
3. Oxygen-bound form has small change in haem (O2 in plane)

Question 42

How do myoglobin and haemoglobin differ? (4)

Answer 42

1. Store in tissue vs transport molecule.
2. Monomer vs tetramer
3. tighter, hyperbolic binding (myo) versus weaker sigmoidal binding (haemo)
4. Haemoglobin has co-operativity