Myoglobin and hemoglobin Flashcards
Bohr effect
An effect by which an increase of a carbon dioxide in the blood and a decrease in PH results in a reduction of the affinity of hemoglobin for oxygen.
Myoglobin structure
MONOMER, right handed helices
- Center heme with 4 pyrrole connected by methyne bridges
- Polar outside
- Non-polar inside
- distal his H7
- proximal his H8
Model of the oxygen binding site
Fe2+: 6 coordination positions 4 occupied by the heme 1 by proximal His 1 by O2
Functions of His
Proximal His: holds the heme
Distal His: bent mode binding of O2–> weakens CO binding
(endogenous CO production
occupy 1% of sites
Hemoglobin structure
a tetramer (a1a2 b1 b2) b subunit has a high homology to myoglobin
T: state
Low O2 affinity, Low PH, BPG, ionic bonds
R:state
high O2 affinity, high PH, no BPG, secondary bonds
Curves myo vs hemo
hemo: sigmoidal
myo: hyperbolic
Triggering the T R conformational change
Deoxyhemoglobin (T form)
Fe2+ is out of the plane of the hemeand
protrude His F8, and the F8 helix
Oxyhemoglobin (R form)
O2 binds to heme and heme becomes planar
and initiation of movement
(His F8 and +F helix)
Fetal Hb
a2g2
His 143 –> Ser 143
weaker BPG binding –> higher affinity for O2
Hg M
proximal His–> Tyr
Ferric Fe3+ instead of Fe2+–>cant delever o2
Water binds instead of O2 –> lethal polyecythemia
Hg S
Glu6–> Val6
causinf sticky patch
sicklecellanemia
Thalassemias:
Alpha and beta are partially absent
defective synthesis of hb
2,3 BPG
Forms saltbridges with Beta subunit stabalizing T-state
Substitutents on beta position of heme
Methyl, vinyl, propionate
