Hemoglobin/Myoglobin Flashcards
What are hemeproteins
Proteins that contain heme as a tightly bound prosthetic group
What is a prosthetic group
Coenzyme that is permanently attached to an enzyme or protein that stays bound and gets recycled to be reused
Name 4 heme proteins
Cytochromes, catalase, myoglobin and hemoglobin
Function of myoglobin
Function of hemoglobin
Used to reversibly bind oxygen - not in the blood stream, its in muscle
Used to reversibly bind oxygen in the blood stream
Structure of heme
Heme can make two additional bonds between what two things?
Fe2+ in middle by bonds of 4 nitrogens of the porphyrin ring
R group of a histidine and oxygen
Presence of oxygen on heme plays an important role for
Relaxed/taut state
Myoglobin
- Located
- 2 functions
- Myoglobin is a single polypeptide similar to
- In skeletal muscle and heart
- Oxygen reservoir, oxygen carrier that increases rate of transport within muscle cell
- Individual alpha and beta globin chains found in hemoglobin
Myoglobin:
- 80% of it is
- Heme group is lined with?
- Function of the two histidines
- What moves faster in the cell: oxygen or myoglobin
- Alpha helix structures
- Nonpolar amino acids except for 2 histidine residues
- One binds to iron of heme; other stabilizes the binding of oxygen to the iron
- Myoglobin; so it helps with the transfer of oxygen- also because it has high affinity
Myoglobin has similar structure of hemoglobin except
Hemoglobin is myoglobin x4
~myoglobin is monomer; hemoglobin is tetramer
Hemoglobin:
- Found where
- Major goal
- Structure
- RBCs
- Deliver oxygen from the lungs to the tissue
- 2 alpha chains and 2 beta chains. Alpha and beta chains are hooked together via hydrophobic interactions (alpha beta dimer associated with another alpha beta dimer)
Hemoglobin
- How many oxygens can hemoglobin transport
- What else besides oxygen can hgb transport
- 4 (from lungs to tissue)
2. CO2 and H+ from peripheral tissues back to lungs
Hemoglobin:
So alpha beta dimer and alpha beta dimer are held together by hydrophobic interactions; how are the two dimers held together
Weaker ionic and hydrogen bonds (amount of polar bonding between the two dimers depends on whether or not oxygen is bound)
- Taut form of hgb has more
2. Relaxed form has more
- Ionic and hydrogen bonds and fewer oxygens are bound (which means less affinity for oxygen)
- Oxygen is bound which causes conformation to bury some charges/R group chains that have hydrogen bonding capability
What drives the relaxation of the bonds between the dimers?
When one O2 binds it changes the conformation, relaxes the bonds and causes the structural change in the rest of the tetramers that holds the alpha helices together and increases the affinity for more O2
Affinity of oxygen is defined by?
P50; 50% of oxygen saturation
How do you move on the graph to represent unloading of oxygen from the heme molecule
Moving down the graph and to the left
As the graph shifts to the right, what is happening to oxygen affinity?
So as p50 goes up (pO2 on x axis), oxygen affinity goes down…why?
Oxygen affinity is going down
Shift to the right means you have to have more oxygen in the environment to have 50% of molecule loaded
Vice versa for left shift
Which has a higher affinity for oxygen: myoglobin or hemoglobin
Myoglobin (so it is more left on the graph)
Is it more common to see a right sided shift or left sided shift
Right sided shift (shifting towards less affinity for oxygen)
Hemoglobin curve
- Y axis is
- X axis is
- Degree of saturation
2. Partial pressure of oxygen where a low p50=high affinity and a high p50=low affinity
If you do not have a high demand for oxygen, then oxygen content in the blood stream at the capillary bed will be high or low?
High - less offloading because you don’t need that much in the tissues
~when exercising, it will be low because your tissues have a higher demand for O2
Shape of myoglobin on the graph
Shape of hemoglobin
Hyperbolic
Sigmoidal
Myoglobin is designed to do what
Bind oxygen at low pO2 found in muscle (releases oxygen in response to oxygen demand)
Explain the heme-heme interaction
If you bind one oxygen, it increases the affinity for oxygen of the remaining heme groups in the same hgb molecule
Name 3 allosteric effectors of heme-heme interaction
(PO2), pH, pCO2, and 2,3-BPG
In peripheral tissues, lower pO2 will allow
Oxygen unloading
Hemoglobin has less affinity for oxygen at what pH (Bohr effect)
Which way will this shift the curve
Lower pH
To the right
Hemoglobin delivers oxygen from site of __ pO2 to __ pO2
When will myoglobin release oxygen?
High to low
At close to zero pO2
Bohr effect
PH is higher in lungs and lower in peripheral tissues; what does this do to the efficiency of hgb as an oxygen transporter
Increases its ability as an oxygen transporter
Bohr effect
Which has a higher affinity for protons: deoxyhemoglobin or oxyhemoglobin
3 features of protonated version
Deoxy
Stroner ionic interactions, more stable taut form and lower affinity for oxygen
2,3 BPG
- Binds to?
- Stabilizes what form
- What does it do to affinity of hgb for oxygen
- Where is the binding site for 2,3 BPG
- Only to deoxyhemoglobin
- Taut form
- Decreases
- In between 2 beta globin chains in deoxyhemoglobin
If you had no 2,3 BPG how would curve shift
To the left (such that it binds oxygen with such high affinity)
What happens to 2,3 BPG levels with chronic hypoxia / high altitude / anemic patients
2,3 BPG levels increase
How is most CO2 transported
Some CO2 is transported as __; this binding stabilizes what form and results in graph shifting to the
In form of bicarbonate ion
Carbamate that forms carbaminohemoglobin; T form; right
CO (carbon monoxide)
- How does it bind to HgB
- Binding supports which form
- Shifts curve to the
- So high O2 affinity and oxygen binding sites occupied by CO results in?
- Tightly (hgb has high affinity for CO)
- Relaxed
- Left
- Critically low oxygen unloading at peripheral tissues
Fetal hemoglobin (HbF)
- Structure
- __ affinity for 2,3 BPG, why?
- __ affinity for oxygen
- 2 alpha chains and 2 gamma chains
- Low - gamma chains lack some postive AAs that the 2,3 BPG interacts with
- High (able to absorb oxygen from maternal circulation
How is HbA1C formed?
By glycolation of HbA - so if you have a lot of sugar in your blood, you will have a high HbA1C
Sickle cell anemia:
- When are symptoms shown
- Symptoms
- Lifetime of these RBCs
- Need to avoid what two things
- Mutation that causes this
- Treatment
- ~6 months of age, when HbF is replaced by HbS
- Pain, hemolytic anemia, increased susceptibility of infection
- Less than 20 days (normal RBC is 120 days)
- Dehydration and extreme exercise
- Glutamate replaced by valine (less negatively charged)
- Hydroxyurea (antitumor drug) - can increase amount of HbF which decreases sickling
Hemoglobin C disease
- Caused by
- Leads to
- Lysine substituted for glutamate
2. Mild chronic hemolytic anemia, no crises, no specific therapy required
Hemoglobin SC disease:
- Caused when
- Symptoms
- When a patient inherits one copy of HbS and one copy of HbC
- Variable; between more severe sickle cell anemia and less severe hemoglobin C disease
