Oxygen Transporters

Question 1

what is myoglobin? what is the iron surrounded by?

Answer 1

the oxygen transporter of muscle

-4 nitrogens

Question 2

describe the pocket that heme is tucked away in and why this is helpful

Answer 2

• non polar pocket, sequestered from water

- helps maintain the iron in a +2 state (nonoxidized)

Question 3

why does oxygen bind more tightly to heme in myoglobin than carbon monoxide?

Answer 3

• steric hinderance

- O2 binds at a 120 degree angle which is preferred, CO binds perpendicularly

Question 4

what happens to the myoglobin protein when O2 binds? what consequence does this have?

Answer 4

it changes shape (not very much)

-this has little to no consequence because REMEMBER myoglobin is monomer!! (no cooperative binding)

Question 5

what general shape is myoglobin?

Answer 5

heical

Question 6

what color is:

• oxygenated myoglobin
• oxidized myoglobin
• deoxygenated

Answer 6

• red
• brown
• blue

Question 7

what are the roles of the two histidines found in myoglobin?

Answer 7

-one binds the oxygen, the other forms a ligand to the iron which moves when oxygen binds

Question 8

what constitutes the subunits of Hb?

Answer 8

2 alpha and 2 beta

Question 9

what is the shape of Hb?

Answer 9

globular

Question 10

how many heme prosthetic groups does Hb have?

Answer 10

4 heme groups

Question 11

what does the hill plot show and what does an n>1, =1, and <1 mean?

Answer 11

• this is a chart that shows if there is cooperative binding in a protein
• n>1 = yes, positive coop
• n=0= no cooperativity
• n<1 negative coop

Question 12

in what range of oxygen pressures does myoglobin work and hemoglobin?

Answer 12

• myoglobin works in low O2 pressures such as muscle

- Hb works best in moderate O2 pressures throughout the body (works over a wider range)

Question 13

Does the T or the R state of Hb bind oxygen more readily?

Answer 13

R (relaxed?), once one oxygen is bound, Hb moves into the R conformation
-the alpha will change the beta that it is tightly associated with and vice versa

Question 14

why does the T form exist?

Answer 14

it is more stable in this conformation when not bound to oxygen

Question 15

why is the T state of Hb more stable?

Answer 15

has more H bonds and electrostatic interactions

-more H bonds between the two ab dimers, specifically

Question 16

How does CO2 effect the binding of Hb to O?

Answer 16

reduces the affinity for O2, allowing Hb to drop off O2 in tissues that have CO2 accumulating

Question 17

what does H+ do to the affinity of Hb to O2?

Answer 17

reduces the affinity, allowing Hb to drop off O2 to tissues that have lactic acid accumulated

Question 18

what is the haldane effect?

Answer 18

deoxygenated blood has a greater capacity to carry CO2 and vice versa

Question 19

by what mechanism does H+ effect Hb?

Answer 19

it is a negative allosteric regulator ( does not bind to heme itself)

Question 20

where does CO2 associate with Hb? what is the result of this binding?

Answer 20

the N terminal a-amino groups

-the carbamate stabilizes the deoxy form of Hb relative to the oxy, making CO2 a negative allosteric regulator

Question 21

does CO2 bind heme?

Answer 21

no

Question 22

how does BPG interact with on Hb?

Answer 22

binds to the beta subunit in a positively charged cavity

Question 23

what affect does BPG have on Hb?

Answer 23

lowers its affinity for oxygen

Question 24

when does BPG rise in the body?

Answer 24

in low oxygen environments (altitude)

Question 25

what is the fetal form of Hb composed of?

Answer 25

a2gama2

Question 26

what binds oxygen with a higher affinity, HbA or HbF?

-why?

Answer 26

HbF

-HbF has fewer positive charges in its corresponding pocket than HbA and HbF binds BPG less well

Question 27

what do the two histidine residues on Hb do?

Answer 27

one forms a ligand to the iron, the other reduces CO binding

Question 28

what are the three negative allosteric regulators of Hb?

Answer 28

CO2, H+, and BPG

Question 29

what creates the sickle chape of sickle cell RBC’s?

Answer 29

insoluble HbS

Question 30

what is the change in amino acid in SS disease and where does this have an effect?

Answer 30

glutamate to a valine on the exterior of the beta subunit

Question 31

how can sickle cell be diagnosed?

Answer 31

electrophoresis of Hb

-glutame (WT) is negatively charged and valine is neutral

Question 32

sickling in SC patients is worse in high or low oxygen conditions?

Answer 32

-low, this is due to a hydrohpobic knob being present on the beta subunits of HbS which fits into the hydrophobic hole of alpha subunits of deoxy alpha subunits (this alpha hole is present in WT Hb as well, but not the beta knob)

Question 33

what were the four treatments of SC discussed in class and their mechanisms?

Answer 33

• antibiotics: prevent secondary infection
• hydroxyurea: stimulates production of HbF which is normal
• BM transplant: replace HbS with HbA
• Gene therapy: works in mice, clinical trials underway

Question 34

what is methemoglobin?

Answer 34

oxidized form of Hb (Fe3+) and cannot carry oxygen.

Question 35

what is the clinical presentation of methemoglobin?

Answer 35

shortness of breath, cyanosis, mental status changes

Question 36

how is methemoglobin diagnosed?

Answer 36

absorption spectrum of the blood

Question 37

the ingestion of what can promote the formation of HbM?

Answer 37

nitrates and nitrites

Question 38

what can help treat HbM?

Answer 38

reducing agents (vitamin C and methylene blue)

Question 39

what is a thalasemia?

Answer 39

an imbalance in the synthesis of the alpha and beta subunits of hemoglobin

Question 40

what ethnicity are thalasemias common in?

Answer 40

mediterranean, some south asian

Question 41

what is the treatment for thalassemias?

Answer 41

blood transfusion

Question 42

a mutation in what subunit of Hb causes SC?

Answer 42

beta