8_9/10_16Hemoglobin and Hemoglobinopathies

Question 1

Hemoglobin (basic structure and function)

Answer 1

4 subunits (2 alpha and 2 beta)
cofactor/prosthetic group = heme, binds ferrous iron 
heme in center to protect from auto-oxidation, contains 4 hemes, one in each subunit
subunits held together by salt bridges

Question 2

Myoglobin v. Hemoglobin

Answer 2

1 v. 4 subunits
Michaelis-Menten v. Allosteric kinetics
P50 for myoglobin is less than for hemoglobin

Question 3

Myoglobin (S and F)

Answer 3

single chain of 153aa, contains a heme, hyperbolic oxygen binding curve, cytosol of muscle cell, aas different than for Hb

Question 4

T v. R state

Answer 4

stabilized by
acidosis v. alkylosis
2,3BPG v. oxygen (allostery)
CO2 v. NO

Question 5

Equations

Answer 5

Mb (no cooperativity)
Y (sat.) = pO2/(pO2 + P50)= [O2]/([O2]+K)

perfect cooperativity
Y=(pO2)^4/((pO2)^4+(P50)^4)

exponent is the Hill coefficient (degree of cooperativity) for Hb this is 2.8

Question 6

Bohr Effect

Answer 6

Acidification shifts curve to right (using Asp, His pH monitor His pKa is 7.1 in R and 8.0 in T states) so at lower pH a salt bridge forms

Carbamide formation in excess CO2 stabilizes T state

NO released with oxygen and causes vasodilation

binding of 2,3BPG stabilizes T state and promotes the release of O2 at PO2 in tissue, it also coordinates conformational changes

Question 7

Hb variants

Answer 7

in adults (HbA 90% alpha beta) (HbF

Question 8

Alleles

Answer 8

4 copies of alpha, 2 of beta

in order of use Ch11 embryonic (epsilon) fetal (gamma) adult (beta, delta) ; Ch 16 embryonic (zeta) fetal/adult (alpha)

Question 9

CO

Answer 9

250x affinity to Heme than O2, but a His residue stabilizes Oxygen through H bonding, smokers have some CO probs

Question 10

Glycation

Answer 10

non-enzymatic
binds at BPG site
diabetes???

Question 11

Sickle Cell Anemia

Answer 11

painful joints, kidney and spleen damage, freq. hosp.
beta chain mutation causes fragile rigid erythrocytes

heterozygosity protects from malaria

Question 12

SCA attack

Answer 12

in high conc. of deoxy HbS

treatments:
chemicals that stimulate production of HbF
bone marrow or stem cell therapy

Question 13

Thalassemias

Answer 13

missing or modified expression of a gene alpha or beta screws with Hb synth.

major, minor or persistence of HbF

in beta thal. alpha chains agg. into Heinz bodies
in alpha thal. beta tetramers form HbH, reduced solubility and no allosteric regulation

Question 14

alpha thal

Answer 14

how many effected 1-carrier, 2- trait, 3-disease 4- hydrops fetalis (death)

results in higher level of Hb Bart’s (gamma4) and HbH (beta 4)

Question 15

beta thal

Answer 15

only beta chains effected
possible higher HbF and HbA2
post natal expression
can be cured by bone marrow transplant

Question 16

Methemyoglobin

Answer 16

promotion of ferric iron binding to heme HbM (Hyde Park)