Oxygen Binding Flashcards
What is the problem with oxygen in regards to the protein side chains?
Animals need to have O2 but protein side chains are unable to bind O2
Why aren’t transition metals used for oxygen bindings in animals?
Although they are able to bind O2, they would cause damage if free in solution
Why isn’t organometallic compounds such as heme used for oxygen binding in animals?
Heme contains Fe2+, and when free, would be oxidized to Fe3+
How is Heme used in oxygen binding?
Heme, bound to a protein, captures oxygen molecules
What is the function of Myoglobin in oxygen binding?
Myoglobin is a protein that is used to store oxygen. It is often found in muscles
What is the function of Hemoglobin in oxygen binding?
Hemoglobin transports oxygen. It is a heterotetramer
When do you express concentrations in terms of partial pressure?
When the molecule that is bound is a gas
What is P50?
P50 is measured in kPa and is the oxygen concentration in which the fractional saturation is 50 (measured like Kd in terms of a graph)
How would you find the partial pressure of oxygen if given the fractional saturation?
fractional saturation = pO2 / (pO2+P50)
What is the relation between myoglobin and carbon monoxide?
CO and O2 are similar in size and shape and therefore are able to fit in the same binding site. CO binds better than O2 because carbon has a filled lone electron pair which can be donated to vacant orbitals on the Fe2+.
Why is carbon monoxide highly toxic?
Carbon monoxide competes with oxygen. Carbon monoxide blocks the function of myoglobin, hemoglobin, and mitochondrial cytochromes involved in oxidative phosphorylation
Why do we have two different proteins to store and transport oxygen?
Affinity changes with pressure changes.
Does hemoglobin have a higher affinity for the partial pressure in the tissue or the lungs?
The lungs
Explain allostery and hemoglobin
Hemoglobin needs an affinity in higher pressure in the lungs and and lowered affinity in the lower pressure in the tissues. To be able to do this, the protein must have multiple binding sites. The interactions between these binding sites is allostery.
What is positive cooperativity?
It is positive allostery. The first binding event increases affinity at the remaining binding sites and is recognized by sigmoidal curves.
What is negative cooperativity?
It is negative allostery. The first binding reduces affinity at remaining binding sites.
What type of cooperativity does hemoglobin have?
positive.
With the first binding event of hemoglobin, do the remaining bind sites have an increased or decreased affinity?
Increased because it is positive cooperativity
What can be said of hemoglobin because of the sigmoid binding curve?
hemoglobin is more sensitive to small differences in O2 concentration between tissues and lungs allowing it to bind oxygen in the lungs (with higher pressure) and release oxygen in the tissues (with the lower pressures).
What does myoglobin’s Kd say about its relation to O2?
Myoglobin’s Kd makes it great at storing O2 at normal tissue O2 levels
What is the T-state of hemoglobin?
The tense or tight state. This is the most stable state and has a lowered affinity for O2
What is the R-state of hemoglobin?
The relaxed state. This is the most flexible state and has a higher affinity for O2.
What state of hemoglobin has the higher affinity for O2?
R-state
What state of hemoglobin is the most stable?
T-state
What state of hemoglobin is the most flexible?
R-state
What state of hemoglobin has the lowered affinity for O2?
T-state
How does BPG regulate hemoglobin?
BPG is form of allosteric regulation. 2,3-BPG binds hemoglobin which stabilizes the T-structure where O2 binding is not preferred
What state of hemoglobin is related to BPG?
T-state
How does 2,3-BPG binding affect O2 affinity?
It lowers the affinity for O2 binding. The binding of 2,3-BPG allows O2 release in tissues and adaption to changes in altitude.
What effect would increased blood BPG have on P50 for hemoglobin?
It would decrease the P50
What would occur if there was no 2,3-BPG?
Hemoglobin would have a binding profile that resembles an exponential curve
What is responsible for the color of blood?
The heme group is a strong chromophore which absorbs light
Why is it important that iron is incorporated into the heme group, rather than the free in the cell?
If heme was free, the iron would be oxidized to the 3+ state.
How is the heme group attached to the myoglobin?
The heme is in the hydrophobic cleft, the heme group is stabilized by hydrophobic interactions
Do the lungs or the tissues have a higher partial pressure?
The lungs
