Allosteric Regulation and Enzymes

Question 1

Hemoglobin

Answer 1

tetramer, two subunits, with heme group
binds O2 cooperatively

R state: higher affinity for O2, more flexible
T state: more interactions, more stable, binding of O2 riggers R conformational change

Question 2

Carbon Monoxide

Answer 2

Hb affinity for CO is 220x greater than O2

highly toxic

Question 3

cooperativity: positive homotropic regulation

Answer 3

for a protein with multiple binding sites

positive: first binding event increases affinity at remaining sites (sigmoidal)
negative: first binding reduces affinity

(homotropic: ligand is also allosteric regulator)

Question 4

O2 binding in Hb

Answer 4

at low pO2 in tissues, O2 lets go, and loads at the high pO2 in the lungs

Question 5

Bohr Effect

Answer 5

decrease in pH = decrease in oxygen affinity (shift right)

lower pH requires greater pO2 to achieve saturation

Question 6

2,3 bisphosphoglycerate

Answer 6

negative heterotropic regulator of O2 (shift right)
present in erythrocytes
stablilizes T states
allows O2 release in tissues at high altitude

Question 7

Sickle Cell

Answer 7

Glu6 to Val in beta chain of Hb, forms binds between Hb and causes sickle shape

Question 8

Methemoglobin

Answer 8

oxidized Hb, cannot bind O2

treat with methylene blue

Question 9

Carbon monoxide

Answer 9

stabilize relaxed state, left shift, hyperbolic