Flashcards in Hemoglobin and Hemoglobinopathies Deck (115):
Is like a little computer, sensing the gasses around it, the pH around it, and the other ligands in the area. Then it computes wether or not it needs to release or bind oxygen
Goes through a breathing motion. As it breathes, it binds an oxygen molecule. Then when it reaches it's destination, it exhales its oxygen and inhales CO2
Per fluorocarbons make liquids at room temperature with very high solubility for gasses such as oxygen. When blood is replaced with this liquid, a rat can breathe in water or in air. This is called
A non amino acid type group
Acts as a dissolver of oxygen
Heme needs to be in blood because by itself, heme is oxidized forming a
u-bridged heme compound with a hyrdrophobic layer on the top and bottom, which will cause them to aggregate out of solution
Two ferrous (2+) hemes can form a bridged complex with oxygen, producing
Non-functional oxidized heme
What do we call reduced Fe 2+ hemoglobin?
Ferrohemoglobin (an oxygen carrier)
What do we call oxidized Fe 3+ hemoglobin?
Hemoglobin is only functional in the
Ferrous state (2+)
What is a synthetic way to make heme and keep it from forming bridged heme aggregates?
-developed for artificial blood substitutes
In the cell, our hemoglobin is not the picket-fence type. So how do we protect heme from being oxidized?
Heme is surrounded by the hemoglobin protein, which prevents oxidation and u-bridge formation
Heme is the O2 binding molecule common to
Myoglobin and Hemoglobin
Once sequestered inside a hydrophobic pocket created by the folded globin polypeptide, heme encounters a protective environment that minimizes
The oxidation of Fe 2+ to Fe 3+
Mutations that lead to anemia do so by weakening the proteins binding to heme, thus making it more likely that
Iron is oxidized, creating nonfunctional methemoglobin
The O2 binding of myoglobin is not optimal for
Which binds oxygen more tightly, myoglobin or hemoglobin?
Enables hemoglobin to deliver oxygen over a range that best suits our needs
Hemoglobins complex structure
The partial pressure of oxygen, where protein sites are half saturated
Oxygenated and deoxygenated blood are different colors because
They absorb at different wavelengths
Measures the absorption of 660nm and 940nm wavelengths in the arteries
If we take ratios of the extinction coefficients at 660nm and 940 nm, what does it mean if the ratio is less than one?
We have more oxygenated blood than deoxygenated blood
A single-chain globular protein of 153 amino acids.
-made up of all alpha helices
Myoglobin is located in the
Cytosol of muscle cells
Binds oxygen that has been released by Hb in the tissue capillaries and has subsequently diffused across cellular membranes
Controls the gasses which can and can not bind heme
-Prevents CO from binding
The E-helix Histidine
What holds myoglobin together?
The hydrophobic effect from the 60 hydrophobic residues
How many circulating globins are there?
How many non-circulating globins are there?
3 (myoglobin, neuroglobin, cytoglobin)
Hemoglobin is essentially four myoglobin subunits coming together. These four subunits interact with eachother and change the
A different globin gene encodes
the alpha and beta subunits
The primary sequence of hemoglobin and myoglobin is actually
Much different (but their structures are almost identical)
What holds hemoglobin together?
Intermolecular salt bridges (ex: btw Asp and Lys)
Why are the intermolecular salt bridges that hold hemoglobin together good?
1.) They don't compete with the hydrophobic interactions in the core
2.) They allow for flexibility
The amount of oxygen bound to hemoglobin by the time it reaches the tissues is
Allows us to sequester more oxygen within the blood
Takes more partial pressure of oxygen to 50% saturate
Ligand binding causes structural rearrangement that
orients enzyme in its active conformation and makes it
easier for next substrates to bind. This describes
Also utilized in protein folding. Once the fold starts, it becomes a chain reaction of folding
When you look at oxygen binding, we are essentially moving from a low affinity state to a high affinity state.
Hemoglobin is in a low affinity state, then the first oxygen binds and
The affinity increases and keeps increasing with each successive oxygen that binds
A measure of the degree of cooperativity
-represented by n in the saturation equation
Hemoglobins high degree of cooperativity enables it to
Pick up more oxygen in the lungs and deliver more oxygen in the body
Favors the T-state
Favors the R-state
The binding of oxygen to a hemoglobin subunit in the T-state triggers a change in conformation to the
When the entire protein undergoes the T to R transition, the αβ subunit pairs slide past eachother and rotate, which
Narrows the pocket between the β subunits
Change little in the transition from the T state to the R state
The structures of the individual α and β subunits
A protein that exhibits changes in ligand (or substrate) affinity under the influence of small molecule
Bind to proteins at sites that are spatially distinct from the active sites and, through long-range conformational change, alter the affinity of the active site for the substrate
Often multi-subunit proteins
May either increase an enzymes affinity for substrate or decrease an enzymes affinity for substrate
What are the two major conformation of hemoglobin?
T and R states
Although oxygen binds to hemoglobin in either state, it has a significantly higher affinity for hemoglobin in the
More stable when oxygen is absent experimentally and is thus the predominant conformation of deoxyhemoglobin
What makes the T-state more tense than the R state?
The T state has an increased number of salt bridges
Describes how hydrogen ions and carbon dioxide effect the affinity of oxygen in hemoglobin
What is the effect on hemoglobin of lowering pH?
When hemoglobin binds oxygen, it releases hydrogen ions. However, at lower pH, there are more hydrogen ions in solution, which prevents hemoglobin from binding oxygen as well. Thus the affinity of hemoglobin for oxygen is lower in acidic pH
What is the effect on hemoglobin of increases pH?
Higher pH increases the affinity of hemoglobin for oxygen. It will bind oxygen more tightly
What effect do high levels of carbon dioxide have on hemoglobins affinity for oxygen?
High levels of CO2 result in the formation of carbonic acid, which decreases pH, thereby decreasing Hb's affinity for oxygen
What effect do low levels of carbon dioxide have on hemoglobins affinity for oxygen?
Low levels of CO2 increase Hb's affinity for oxygen
What serves as the pH sensor on Hb?
Asp 94 and His 146 on the β chains far from heme binding sites
Why is the T state favored at lower pH?
His 146β gets protonated and becomes positively charged, resulting in salt bridge formation with Asp 94β. This interaction stabilizes the T state
Why is the R state favored at higher pH?
Histidine 146β is deprotonated, breaking the salt bridge with Asp 94β, thus relaxing the protein and stabilizing the R state
In the lungs, Hb releases a proton as it binds O2, the proton reacts with bicarbonate, reforming carbonic acid. This results in
CO2 liberation and water formation
Some CO2 is transported directly with Hb by forming
Carbamates with amine groups on the N-terminus
When hemoglobin goes from the R state to the T state, two free amines are exposed. The amines can bind CO2, forming a carbonate. This stabilizes the
Promotes the excretion of bicarbonate in the kidneys
How can we use Diamox (acetazolamide) to treat altitude sickness, which is caused by a decrease in oxygenation of the bodies tissues at high altitudes.
When bicarbonate is excreted in the kidneys, blood pH drops. This drop in blood pH decreases the affinity of hemoglobin for oxygen, which improves Hb's ability to deliver oxygen to the body
Binds to the R state of Hb directly on the heme iron, as well as a thiol-nitrosyl bond on Cys 93β
Release of Nitric oxide upon deoxygenation of Hb allows NO to?
Bind vascular endothelium receptors, triggering vasodilation and increased blood flow to hypoxic tissues
A normal product of glycolysis in erythrocytes that is critical to the release of oxygen from hemoglobin
Binding of 2,3-Biphosphoglycerate (2,3-BPG) to Hb does what?
Stabilizes the T state and reduces affinity for oxygen
Without 2,3-BPG, hemoglobin acts just like
What affect does acidification of blood have on myoglobin?
How does 2,3-BPG stabilize the T-state and reduce hemoglobins affinity for oxygen?
Forms a network of salt bridges between the two β subunits
What three things stabilize the T-state?
-decreases Hb's affinity for oxygen?
1.) Low pH
2.) 2,3, BPG
3.) High levels of CO2
What three things stabilize the R-state?
-Increases Hb's affinity for oxygen
1.) High pH
2.) Oxygen (allostery)
3.) Nitric oxide
The varying Hb's are arranged on chromosomes in the order of
Their expression during development
Instead of being composed of 2α and 2β subunits, fetal hemoglobin is composed of
2α and 2ƴ subunits
Has a lower affinity for 2,3-BPG
-Has a higher affinity for oxygen
There are two very important Histidine's in Hb. The distal histidine binds the Fe 2+. What does the other (known as the E helix) do?
Sits on the top side of the Fe 2+ and destabilizes CO binding while at the same time stabilizes oxygen binding
A colorless, odorless gas responsible for more than half of annual poisoning deaths worldwide
Carbon Monoxide (CO)
How much greater of an affinity does CO have for Hb than oxygen?
Produces cherry red discoloration of the skin and organs
-treated with 100% or hyperbaric oxygen
Glucose can be added to the N-terminal of the beta chains of Hb, resulting in
Glycation of Hb by glucose to HbA1c
Glycation of Hb by glucose to HbA1c is a relatively irreversible reaction which affects the binding of
Representative of glucose over 6-8 weeks, making them a good indicator of diabetes risk or the efficacy of current treatment
Affects the electrophoretic mobility of Hb
When Hb sickles it can cause red blood cells to rupture, which can result in
Blockages and Ischemia
In people with Sickle Cell Anemia, Red blood cells are more
Fragile than normal
An autozomal recessive (AR) disorder that is a homozygous condition
Sickle Cell Anemia
You can be heterozygous for sickle cell and not have full blown sickle cell anemia. This is called having the
Sickle Cell Trait
Usually asymptomatic, except in the renal medulla where oxygen tensions are low enough to induce sickling and renal damage
Sickle cell trait
Butyrate and hydroxyurea stimulate the production of HbF, why might this be an effective treatment to alleviate the presentation of sickle cell?
HbF brings in healthy beta chains in the form of Y chains
What are two other methods to treat sickle cell?
1.) Bone marrow stem cell transplant
2.) Gene therapy
Individuals heterozygous for sickle cell are protected against the most lethal forms of
Part of the life cycle of the malaria parasite plasmodium is spent reproducing in red blood cells, however, free Hb is toxic to plasmodium so it sequesters Hb into a crystalline form called
Many anti-malarials disrupt
Infection of RBCs by plasmodium triggers sickling, recruiting phagocytes that then clear the infected cells in
A Glu 6 Lys mutation that causes intracellular crystallization of Hb and cation leak, resulting in dehydration
Genetic disorders of Hb synthesis
What are the three main causes of Thalassemias?
1.) Hb gene is missing
2.) Gene is present, but expression is impaired
3.) mRNA is produced, but it encodes disfunctional Hb
Thalassemias caused by impaired expression of the Hb gene are due to
Modifications to gene promoter region
What causes the Thalassemias where the mRNA is produced but it encodes grossly disfunctional Hb?
Introduction of an early stop codon
In β-thalassemias, α-chains aggregate into
The β4 tetramers form (HbH) which has reduced
solubility and lacks allosteric regulation found in HbA
What are the four types of α-thalassemias
1.) Silent carrier
4.) Hydrops fetalis (death occur because no alpha chains)
β-thalassemias have higher levels of
HbF or HbA2
α-thalassemias have higher levels of
Hb Barts: y4, or HbH
The nonfunctional oxidized version of hemoglobin
-often manifests in cyanosis (blue lips, extremities)
Higher than noirmal (> 1%) levels of oxidized hemoglobin
Methemoglobinemia can be induced by certain
Effects interactions with cytochrome-b5-reductase and can lead to methemoglobinemia
HbM (Hb Hyde Park) mutations
Can be used to treat cyanide poisoning by oxidizing Hb, which readily binds cyanide, producing cyanohemoglobin.