BIOCHEM: Hemoglobin

myoglobin

- oxygen storage protein

- single polypeptide

hemoglobin

- Oxygen transport protein

- tetrameric protein

- 4 myoglobin is what it basically consists of

Fe(II)

- This is a strong tendency to bind oxygen

- chelated to tetrapyrrole ring system

protoporhyrin IX

What is the name of the tetrapyrrole ring system?

Heme

- Deals with Fe being non covalently bound in a hydrophobic pocket

proximal histidine

- This is the histidine that is in direct contact with Fe

distal histidine

This is the histidine that is not in direct contact with Fe

- this one holds the oxygen in place

Picture of proximal and distal histidine

hyperbolic

The binding curve for myoglobin binding to oxygen is ______________

means 1 P50 only

P50

This is the partial pressure of oxygen where half of the binding sites are bound

You do not need very much oxygen pressure in order to bind 50% of the sites

What does having a low P50 mean?

HIGH binding affinity

If you don't need a lot of oxygen pressure in order to bind to sites then what does that mean?

high

If you have a low P50 then you have a ___________ affinity.

Requirements of oxygen transfer

1. Accept oxygen efficiently at partial pressure found in the lungs (100 mm Hg)

2. Upload a fraction of O2 to tissues (30 mm Hg)

- Cannot be hyperbolic binding

- Must be sigmoidal - this means it is allosteric

True

True or False: Oxygen transport by hemoglobin is allosteric meaning the P50 can change

sigmoidal curve

Cooperative binding

a type of allostery

known as the allosteric switch

deals with the binding of multiple things

conformational change

Cooperative binding results from ____________ in the protein causing the affinity of the binding site to increase.

photo of oxygen transfer being allosteric

binding

There is an increase of O2 affinity with O2 ___________.

Deoxy (T) Hemoglobin

- shows a change in quaternary structure (TENSE)

- this structure deals w/ low affinity for O2 and salt bridges forming (high P50)

Oxy (R) Hemoglobin

- this structure deals w/ high affinity for O2 and salt bridges NOT forming

- O2 is bound to it

Deoxy overlaps compared to Oxy

Deoxy has a bigger hole in the middle (allosteric site)

From the photo what is difference between Deoxy and oxy hemoglobin?

communication between hemoglobin sites

Relationship of His F8 and neighboring Val to heme in deoxyhemoglobin demonstrate the change in conformation associated with the T to R transition – change in secondary structure causes a change in tertiary

strain

_________drives conformational change in the communication between hemoglobin sites when oxygen binds to it.

C02

- another allosteric ligand of hemoglobin (oxygen is the other one)

- This accumulates in erythrocytes and lowers the PH

increase

As PH low we see the efficiency of oxygen unloading _____________

- His forms salt bridge with Asp in the deoxy form which increases the pKa of the His by stabilizing the protonated (positive) form

- Salt bridge does not form in the oxy form, lowering the pKa

When the PH lowers why does the efficiency of oxygen unloading increase? ITSCALLED THE BOHR EFFECT

KNOW THESE PROPORTIONS

increase of CO2 binding

decrease of pH

increase of P50

increase of oxygen unloading (will not bind with as much affinity)

know this photo

know this photo

Diphosphoglycerate (BPG)

- Acclamation (adjustment)of lower oxygen pressure of high altitude over time due to increases of production of hemoglobin and changes in amount of BPG

- has a more efficient unloading of O2

- stabilizes deoxy form

lowers

The binding of BPG ___________ O2 affinity of Hb.

True

True or False: BPG cannot bind to the oxy form of hemoglobin.

True

True or False: Both CO2 and O2 and BPG are all allosteric effectors.

photo of BPG

BPG and how it deals w/ fetuses

A fetus obtains oxygen from mother's blood; must have higher O2 affinity

- Adult hemoglobin (HbA) is α2β2

- Fetal hemoglobin (HbF) is α2γ2

- Lower affinity for BPG

- Replacement of His 143 with Serine

HbA

Does BPG bind better to HbA or HbF?

Sickle Cell Hemoglobin

- This is caused by the aggregation of deoxyhemoglobin and the blockage of capillaries

Mutation that deals with the cause of sickle cell hemoglobin

Glutamic acid to valine (hydrophobic amino acid which fits into a hydrophobic pocket causing hemoglobin molecules to "lock" together

metabolism

If you have a higher Km (shifted to the right) then reaction won't work as well and slows __________ (INHIBITION)

QUESTION WILL BE ON FINAL FOR THIS