Biochemistry: Myoglobin and Hemoglobin (Test 2)
β-Thalassemia
β globin is lost or cannot be expressed Homozygous: rely on gamma chains Heterozygous: one β gene is functional
Valine in Sickle cell does not want to be exposed to the aqueous environment (hydrophobic) therefore
it begins to clump
When oxygen binds to hemoglobin, it is hard to detect which model is happening because ____________ .
it happens so quickly
Allosteric Enzymes possess _________________
quaternary structure
BOHR effect is the
response of Hb to a change in pH and CO2
R form is stabilized by (4 things)
1. Binding of oxygen to Heme group 2. release of 2,3-BPG 3. Increase in pH 4. Decrease in CO2
Partial pressure of oxygen (pO2) in the lungs is
100 torr
Hemoglobin with __________ is going to release more oxygen
2,3-BPG
At biological pH, oxygen release is about ______ in tissues
66%
Sickle Cell Anemia happens because
A change from Glutamic Acid to Valine (going from a negative charge to a neutral charge) (Glutamic is hydrophilic, Valine is hydrophobic)
In order for beta chains to come together, there is __________
A change in the quaternary structure and some changes on the tertiary structure.
Binding of Iron (Fe2+) to oxygen causes what:
Histidine is pulled into ring plane and Histidine with helix shifts position, disrupting some ion pairs between subunits.
The iron ion lies slightly ________ the plane of the porphyrin in deoxyhemoglobin heme, but _________the plane of the heme on oxygenation.
Outside, Moves into
Transition from Deoxyhemoglobin (T state) to oxyhemoglobin (R state) occurs upon ________________ .
Oxygen Binding
High pH promotes
Oxygen binding (stabilizes R state)
Low pH promotes
Oxygen release (stabilizes T state)
______________ CANNOT accommodate 2,3-BPG
R state
It takes __________________ to saturate hemoglobin to 50% at ____________
higher pressure higher altitudes
In the gamma chains of Hb F, the _______ is replaced by _________
histidine serine
The binding of oxygen to myoglobin follows a _____________ curve
hyperbolic
As the oxygen begins to bind to the iron, the cavity itself begins to ___________
shrink (deoxyhemoglobin to oxyhemoglobin)
5th coordination site
occupied by an imidazole ring of a histidine called the proximal histidine.
The structural features are similar in myoglobin and hemoglobin for different animals because
of the amino acid sequence (amino acids are conserved between species
______________ is a allosteric stimulator
oxygen
There is a direct correllation between BPG and
p50
Gamma chain does not have as many __________
positive charges
The heme group consists of a organic group, ________________, and a _________________ .
protoporphyrin, central iron ion in the ferrous (Fe2+) form
At normal pH of 7.4
salt bridges do not form between His and Asp.
If the interacting sites bind different ligands
Heterotropic effect
Low P50 signifies
High affinity for oxygen
Allosteric activators binding to a site separate from the functional site leads to
Active (R state)
Describe adult hemoglobin (Hb A)
Adult chain is mainly beta chains, this attracts negatively charged 2,3-BPG.
The fraction of the myoglobin sites bound to the oxygen depends on the ________________ .
Concentration of the free oxygen
Subunits are either all T state or all R state
Concerted model
Once iron is bound to oxgen, what occurs
Conformational change in hemoglobin (cavity shrinks, becomes narrower). This dictates between deoxyhemoglobin and oxyhemoglobin
Describe fetus hemoglobin (Hb F)
Has gamma chain (α2ϒ2), it supports the R state, it has a serine group(LOSING POSITIVE CHARGES) instead of a histidine group, it has low affinity for 2,3-BPG. Oxygen binds more tightly to fetal Hb
If the interacting sites bind ALL the same ligand
Homotropic effect
Allosteric inhibitors binding to a site separate from the functional site leads to
Inactive (T state)
Name some of the functions of myoglobin (3)
Increase O2 solubility in tissues (muscle), Facilitates O2 diffusion, stores O2 in tissues
Look at slide 25 in Lecture 8 to understand variants for sickle cell
Look at slide 25 in Lecture 8 to understand variants for sickle cell
Sickling occurs when
there is a high concentration of deoxy Hb
Oxyhemoglobin is
(R state)
Deoxyhemoglobin is
(T state)
Purified Hb or stripped Hb doesn't have
2,3-BPG
pO2 in the tissue is ______________
20 torr
Iron lies in the middle and can form __________________, and two additional bonds called __________________
4 bonds with nitrogen 5th and 6th coordination sites
Iron in Heme is bound to six sites, what are they?
4 nitrogens, a nitrogen from a proximal histidine side chain on one of the main acids in the protein, and the last coordination site (6th) is available to bind to a O2 molecule.
____________________ is the binding of one ligand to a protein influences the affinities for the ligand of the other binding sites on the protein
Allosteric Effect
Bind to a protein at a site separate from the functional binding site (may be inhibitor or activator)
Allosteric effectors (modulators)
How does a low pH cause more O2 to be released?
At a pH of about 7.2, salt bridges (ionic bonds) form between histidine and aspartic acid. This stabilizes the T state (deoxy) of Hb. Therefore more oxygen can be released.
Allosteric effectors of hemoglobin are: (3)
Biphosphoglycerate, Protons, CO2
Alpha-Thalassemia
Can have 0,1,2,3, or 4 copies of alpha chains Low levels of alpha chains are compensated with gamma or beta tetramers
Stabilizes the T state of Hb (CO2 as an allosteric effector)
Carbamate (salt bridge)
What is an example of an allosteric effect?
Cooperative binding of oxygen in hemoglobin
Distal Histadine, why is it important
Distal histadine is opposite to the proximal histadine. It is responsible for preventing oxidation of Heme iron and reduces CO from binding to heme (Distal histadine is responsible for stabilizing oxygen found in 6th coordination site.
What is pO2?
Fraction of gas phase that is O2 (pressure)
Describe the structure of hemoglobin
Heterotetramer: 2 alpha subunits and 2 beta subunits (M.W.= 64 KDa). Alpha and beta subunits are homologous (similar) to each other and to myoglobin. Myoglobin binds 4 oxygen molecules
β chains have His at central cavity BUT γ chain has serine residues So what does that mean for binding affinity for BPG?
Hb F has a lower binding affinity for 2,3-BPG, therefore, it can bind more tightly to oxygen as oxygen is delivered from the maternal to the fetus
The addition of iron to a protoporphyrin IX ring turns causes the ring to know be known as
Heme (Iron has to be in Fe2+ state)
You want primary oxygen carrier to be _______________. What type of curve will this have?
Hemoglobin Sigmoidal
T form is stabilized by (4 things)
Increase in CO2 Decrease in pH Oxygen being released from heme group Binding of 2,3-BPG
Describe the structure of myoglobin
Monomeric protein (single polypeptide chain), globular protein, intracellular protein (mainly in muscle cells) Myoglobin only binds one molecule of oxygen. Has two components: oxymyoglobin and deoxymyoglobin (16KDa), 78% alpha-helical structure
Higher amounts of CO2 cause what?
More oxygen to be released into the tissues (ex. if two examples have the same pH, but one has a higher pressure of CO2, the one with the high pressure of CO2 will release more O2)
2,3-BPG is __________ and binds to ____________ amino acids between ____________
Negatively charged, positively charged, β subunits
Conformational changes of hemoglobin chain are induced by ___________.
Oxygenation
Partial pressure of O2 required to give 50% saturation.
P50
Sickle cell anemia can lead to ______________________ (can lead to diabetes, heart failure, liver disease)
Secondary hemochromatosis
Binding of S converts only that subunit from T to R
Sequential model
2,3 BPG and CO2 both stabilize ______________
T state
2,3-BPG binds only to ______________
T states
Misfunctioning of hemoglobin genes
Thalassemias (One or more genes coding for hemoglobin have been deleted, one or more genes may be shortened)
Name a function of hemoglobin
Transports O2 from lungs to peripheral tissues (erythrocytes)
Allosteric enzymes have a rapid transition between the ____________________ and the ____________________ conformations
active (R) inactive (T)
Mutation in sickle cell anemia is found on the ____________
beta chain
6th coordination site
binds to oxygen
Whenever _____________ contain one or more oxy subunits, the T----> R transition occurs
both αβ dimers
Structure dictates __________ .
function
Beta chain ________________ after the baby is born
greatly increase
Only ________________ can be in both R and T conformations
hemoglobin
2,3-BPG increases at ____________________
higher altitudes
Decrease in pH (increase in H+ concentration) promotes an _________________
increase in oxygen release
Fe3+ acts as an __________________ to oxygen binding
inhibitor
Activities of allosteric enzymes are changed by ______________ and _________________
inhibitors activators
What structural changes occur when oxygen binds in Hemoglobin?
iron ion moves into the plane, and the proximal histidine, which is part of a alpha helix, moves with the iron.
As 2,3 BPG increases, _____________________
more oxygen goes into the tissues
The binding of oxygen to hemoglobin follows a _____________ curve
sigmoidal
The resulting structural change(from T to R state) is communicated to the other subunits so that:
the two αβ dimers rotate with respect to one another, resulting in the formation of the R state.