Hemoglobin, Myoglobin O2 Binding Flashcards
Describe myoglobin in 4 points
- O2 carrier in muscle cells
- Stores O2 in muscle cells
- Delivers O2 to mitochondria
- Binds O2 at low O2 levels
Describe hemoglobin in 5 points
- Oxygen carrier in the blood
- Binds O2 in lungs (pO2 ~ 100 mm Hg)
- Releases O2 in the tissues (pO2 ~ 20 mm Hg)
- Sensitive to small changes in O2 levels
5, Carries CO2 from the tissues to the lungs
In lungs, CO2 is…
Released
RBCs in lungs…
High O2 levels favour O2 binding Hb
RBCs muscle…
Lower O2 levels favour release of O2 from Hb
In muscle, Mb, with its higher affinity for O2…
Takes up O2
As mitochondria oxidize fuel, they consume ____ and produce ____
O2; CO2
CO2 is released into the blood and…
Is transported as HCO3 or Hb-CO2
What do active sites of Mb and Hb contain?
A heme
Heme contains a ____ ____ with a single iron atom
porphyrin ring
The Fe can form what?
6 coordinate bonds (4 with pyrrole N in porphyrin ring plane; 1 with imidazole N from His in polypeptide chain; 1 with ligand (O2 or CO)
What does O2 only bind in the heme?
Reduced iron (Fe 2+)
Which heme doesn’t bind O2?
Fe3+ heme / methemoglobin HbMet
How many O2 binding sites does Mb have?
1
How many heme groups does Mb have?
1, which binds one molecule of O2
How many O2 binding sites does Hb have?
4
How many polypeptide chains does Hb have?
4, each with heme to bind an O2
Due to its ____ affinity for O2, Mb would release ________ O2 between 10 and 100 mmHg of O2
high; very little
Due to its ___ affinity for O2, Hb can release _____ O2 between 10 and 100 mmHg of O2
low; more
O2 binding to Hb displays what?
Positive cooperativity
Mb is more or less responsive to changes in O2 conc?
less responsive
What shaped curve is characteristic of positive cooperativity?
sigmoid shaped curve
How many ligand binding sites do you need for + coop?
At least 2
How many receptor confirmations do you need for + coop?
At least 2
Does the first ligand bound have higher or lower affinity than subsequent ligands?
Lower, e.g. larger Kd
What confirmation has a low affinity for O2?
T or taut
What confirmation have a high affinity for O2?
R or relaxed
Where is T prevalent?
At low O2 in tissues
Where is R prevalent?
At high O2 in lungs
Interface of ____ _____ different in R and T state
alpha/beta dimers
Where is Fe in absence of O2?
Out of heme plane, which stabilizes T confirmation
Where is Fe in presence of O2?
Pulled back into the heme plane, which stabilizes the R confirmation and high affinity binding at other O2 binding sites
Hill coefficient for Mb-O2 binding
1
Hill coefficient for Hb-O2 binding
> 1
Positive cooperativity is a form of…
Allostery
What kind of modifier is O2?
Homotropic allosteric modifier
Heterotropic allosteric modifiers are…at the active site
Heterotropic allosteric modifiers are different from the ligand at the active site
Heterotropic inhibitors stabilize which form of the active site?
low affinity form
Heterotropic activators stabilize which form of the active site?
high affinity form
List the 3 heterotropic inhibitors of O2 binding to Hb
pH (H+)
CO2
BPG
An decrease in pH….
Decreases the amount of O2 bound to Hb
H+ does not bind to…
O2 site (e.g. does not bind to Fe in heme)
What does H+ bind to?
His146 in the beta subunit, stabilizing an ionic bond (His146-Asp94) in the T-state
What happens when H+ is lowered and pH is raised?
Ionic bond between His146 and Asp94 is lost and R-state becomes more stable
What kind of bond does CO2 form in relation to Hb? What does this reaction release?
A covalent bond with terminal amine group of Hb. This reaction releases H+
When CO2 binds with terminal amine group of Hb, the terminal carbamino group does what?
Stabilizes the T state
What is BPG?
Byproduct of anaerobic glycolysis (RBCs only support glycolysis)
Where does BPG bind Hb?
At a site distant from O2 binding site
CO poisoning causes how many yearly poisoning deaths world wide?
1/2
What does CO compete with in Hb?
O2 for heme site
Who is susceptible to CO poisoning?
Fetuses
CO binding at Hb active site has ___ and ____ effects
non-allosteric; allosteric
What is an allosteric effect of CO bound at active site
CO bound at active site increases O2 binding at other active sites
What is a non-allosteric effect of CO poisoning?
CO competes with O2 binding at the active sites
What is the major adult form of Hb?
Hb A
Composition of Hb A
alpha2beta2, 95% to 98%
What is the minor form of Hb?
Hb F
Composition of Hb F?
alpha2gamma2, 0.8% to 2%
What is the major Hb in fetus and newborn?
Hb F
Which form has a higher affinity for O2? Hb A or Hb F?
Hb F
Which type of Hb doesn’t bind well to BPG?
Hb F
What is the Sickle Cell form of Hb?
Hb S
Describe Hb S
beta 6 Glu -> Val (alpha2betas2) )%
Describe Hb M
beta59 His -> Tyr (alpha2betam2) 0%
Describe thalassemia
Mutations lead to impaired synthesis of alpha or beta chains
Complete lack of alpha chains usually fatal in utero
What kind of mutation is in Sickle Cell Anemia?
Missense mutation in beta globin gene
In Hb S mutation from Glu to Val, How many negative charges are lost?
2
In the T-confirmation, beta Val-6 on Hb surface exposes what?
hydrophobic patch
HbS associates via what?
Hydrophobic patches
What give RBCs their sickle shape?
Insoluble fibers of HbS polymers
What happens to HbS especially under anoxic conditions?
HbS polymerizes, forming long strands
Because sickle cells are more fragile, what results?
Anemia because of hemolysis, thereby fewer RBCs
HbS forms ___ fibers on deoxygenation
insoluble fibers (gives RBCs sickle shape)
What leads to inflammation in Sickle Cell Anemia?
Free heme and broken RBCs
What occurs in a vaso-occlusive crisis?
Severe pain, inadequate O2 (ischemia) and uncontrolled cell death (necrosis)
Sickle cells are ____ _____ and highly _____
Sickle cells are less flexible and highly adhesive
Due to the limited flexibility and high adhesive nature of sickle cells, what occurs in the body?
It occludes blood flow (infarct) to almost every oran in the body
What are 6 contributing factors to SCD?
- Desoxygenation*
- Dehydration*
- Fever
- Stress situation
- General anaesthesia
- Acidosis*
What chromosome mutation leads to SCD?
Mutation of chromosome 11
Desoxy-Hemoglobin formation (HbS) -> _______ -> Insoluble HbS polymers
Desoxy-hemoglobin formation (HbS) leads to
Lower O2 partial pressure and polymerization, which leads to
Insoluble HbS polymers
Insoluble HbS polymers lead to which 2 things?
- Reduced deformation of RBCs & vaso-occlusion
- Rigidification and fragmentation of RBCs
What 3 things stem from reduced deformation of RBCs & vaso-occlusion?
- Osteonecrosis
- Bone infarction
- Osteomyelitis
What happens after rigidification & fragmentation of RBCs?
Hemolysis:
1. Anemia fewer RBCs (mucosal pallor)
2. Free heme (discolouration of gingiva)
3. RBC membrane, free heme released (inflammation)
What 5 things can happen when there is reduced blood flow/O2 in SCD?
- Osteomyelitis, Orofacial pain
- Atrophy lingual papillae
- Pulpitis, pulp necrosis
- mental nerve neuropathy
- Asplenia - impaired immune system
Pallor of oral mucosal happens with…
Chronic hemolysis, decreased RBCs
Atrophy of lingual papillae happens with…
Vaso occlusion and decreased blood flow
What leads to neuropathy of the mental nerve and labial hypoaesthesia (NCS)?
Vaso occlusion and ischemia of the inferior alveolar nerve
What leads to pulpitis and necrosis?
Vaso occlusion and ischemia of the pulp microcirculation
