Chapter 7. Hemoglobin: Portrait of a Protein in Action Flashcards
An organic constituent of the heme prosthetic group; consists of four pyrrole rings joined by methylene bridges and contains various side chains.
Protoporphyrin
A histidine in globins that forms a hydrogen bond to the bound oxygen that helps to prevent the release of superoxide anion.
Distal histidine
An allosteric effector of hemoglobin that decreases the affinity of hemoglobin for oxygen.
2,3-bisphosphoglycerate
A member of the globin family expressed throughout the body.
Cytoglobin
CO; A colorless, odorless gas that binds to hemoglobin at the same site as oxygen and thereby prevents oxygen binding.
Carbon monoxide
An enzyme that catalyzes the reaction of carbon dioxide with water to form carbonic acid.
Carbonic anhydrase
Hemoglobin that consists of two a chains and two a chains that has a higher affinity for oxygen than hemoglobin A. This difference in affinity allows the transfer of oxygen from the mother to the fetus.
Fetal hemoglobin
A model explaining the kinetics of allosteric enzymes in which the transitions of all of the active sites between the T state and the R state occur simultaneously.
Concerted model (MWC model)
A property of allosteric proteins wherein the reactions at different sites are not independent of one another.
Cooperative binding
An organic compound the results from the reaction of carbon dioxide with the amino groups in proteins. Carbamate formation in hemoglobin reduces oxygen affinity of hemoglobin
Carbamate
The observation made by Christian Bohr that H+ and CO2 promote the release of oxygen from oxyhemoglobin.
Bohr effect
A complex of carbon monoxide and hemoglobin that does not bind oxygen.
Carboxyhemoglobin
The prosthetic group of myoglobin and hemoglobin as well as other proteins; consists of an organic constituent, protoporphyrin, and an iron atom.
Heme
A brain-imaging technique that takes advantage of (1) the fact that magnetic properties of oxyhemoglobin and deoxyhemoglobin are different and can thus be distinguished and (2) the fact that, when a specific part of the brain is active, blood vessels relax and allow more blood flow. Thus, a more active part of the brain will be richer in oxyhemoglobin.
Functional magnetic resonance imaging (fMRI)
The fraction of possible binding sites of a biomolecule that are occupied.
Fractional saturation
A plot of the fractional saturation of oxygen binding proteins versus the concentration of oxygen.
Oxygen-binding curve
Myoglobin in which the iron of the heme is in the ferric state (Fe³+;) and thus cannot bind oxygen.
Metmyoglobin
The fraction of the total pressure of a mixture of gases that is due to one component of the mixture.
Partial pressure
One of the protein subunits of hemoglobin. Hemoglobin is composed of two α chains and two β chains.
β chain
A folding structure of a polypeptide chain, exemplified by myoglobin and hemoglobin subunits, that creates an environment for a heme group to reversibly bind oxygen.
Globin fold
A reactive oxygen species that can damage many biological materials.
Superoxide anion (O2-)
One of the protein subunits of hemoglobin. Hemoglobin is composed of two α chains and two β chains.
α chain
A model for explaining allosteric enzymes in which the binding of one substrate influences the substrate affinity of neighboring active sites without necessarily inducing a transition encompassing the entire enzyme.
Sequential model
Activity curves, such as for oxygen binding or enzyme activity, that show low activity with respect to the x-axis initially and then increase rapidly, thereby generating an “S” shaped curve.
Sigmoid
Hemoglobin, which forms in the absence of the α chain, that consists only β chains. Hemoglobin H binds oxygen with high affinity and displays no cooperativity.
Hemoglobin H
The less active state of allosteric proteins, which is in equilibrium with the more active R-state.
T state
a mutant form of hemoglobin and the cause of sickle cell anemia that aggregates when the oxygen concentration is low, which in turn causes the red blood cells to form sickle shapes that impede blood flow in capillaries.
Hemoglobin S
The more active state of allosteric proteins, which is in equilibrium with the less active T-state.
R state
Anemia caused by a mutation in hemoglobin that promotes aggregation of the hemoglobin when oxygen concentration is low, which in turn causes the red blood cells to form sickle shapes. Such deformed cells to not remain in circulation, thus accounting for the anemia.
Sickle-cell anemia
A disease carried by a mosquito parasite, Plasmodium falciparum, that lives within red blood cells at one stage in its life cycle. The presence of one allele for hemoglobin S confers resistance to malaria.
Malaria
Genetic disorders characterized by the defective synthesis of one or more hemoglobin chains.
Thalassemia
A severe form of anemia that results from the total absence of the β chains of hemoglobin.
Thalassemia major (Cooley anemia)
A member of the globin family expressed primarily in the brain, where it appears to protect against hypoxia (insufficient oxygen).
Neuroglobin
A plot of log(Y/1-Y) versus log(pO2), where Y is fractional saturation and pO2 is partial pressure of oxygen, that can be used to determine the degree of cooperativity of oxygen binding.
Hill plot
The slope of the line generated by a Hill plot. The Hill coefficient is a measure of cooperativity in ligand binding.
Hill coefficient
This histidine in myoglobin and hemoglobin that coordinates to the iron in porphyrin through its imidazole ring.
proximal histidine
Individuals with one copy of the HbA gene and one copy of the HbS gene are said to have this trait because they can pass the HbS gene to their offspring.
sickle-cell trait
A red blood cell protein that binds to the α chain of hemoglobin to ensure the proper folding of the a chain. AHSP is subsequently displaced by the β chain.
α-hemoglobin stabilizing protein (AHSP)
