Haemoglobin and Myoglobin Flashcards
Myoglobin primary
~150 a.a
Myoglobin secondary
8 ⍺-helices
Myoglobin tertiary
Fold with hydrophobic pocket (Val E11 & Phe CD1)
Haem binds to HisF8
Hydrophobic pocket prevents
Oxidation to Fe3+
Haem
Cofactor
Fe2+ (reversible)
Myoglobin quad
Monomeric
Haemoglobin structure
Tetramer
4 goblin proteins non - covalently
1 haem - binds 1 O2
M O2 release
Low O2
HisE7, oppo haem
Distorts O2 binding
Easier to release, lower affinity
M storage
In muscle
M curve
Hypobolic curve
Saturated at low O2 until too low, all released (steep drop)
H T and R state shape
T - dished haem
R - O2 flattens haem, pulls HisF8 and helix F to binding site, increase O2 binding
Anything that pulls helix F away = weakens oxygen binding
T / R stablisation
Steric and polar interactions
H curve
Sigmoidal curve
Bind in lungs (high partial pressure ~100 Torr)
Release in peripheral tissue (low partial pressure ~20 Torr)
Absorbance eq
log(I𝗼/I)
Beer - Lambert Law
A = EcL
E unit
Lmol-1cm-1
Beer’s
Decrease in intensity of transmitted light as conc increase
Lambert’s
Decrease in transmitted light as pathlength increases
Standard curve
Pass orgin
No greater than 1.0 (dilute if needed)
H cooperativity
Influences to be either R or T, all in same state
MWC model
Only explains positive cooperativity (increase affinity, shift to T doesn’t decrease affinity)
Each bind shifts equilibrium to R
KNF model
Negative copperativity (T state influences others, easier release) T -> R influences neighbouring subunits = easier to bind O2
T
Low affinity - hard binding
R
High affinity - easy binding
BPG what is it?
Allosteric inhibitor
Binds to deoxy-Hb by electrostatic interactions
Produced in peripheral tissue
BPG effects
Stablises T state, decrease O2 affinity
Rightward shift
CO2 effects
Decrease O2 affinity by decreasing pH (N terminal H+ protonate a.a side chains)
Stabilise T-state
Feoetuses alternate isoforms
𝜻 = ⍺
𝛜 & γ = β
alternate isoforms why?
Higher affinity
Feoetuse benefit
Lack a.a that binds BPG
Methaemoglobin
Fe2+ -> Fe3+ O2 doesn’t bound
Shifts subunit into R state, doesn’t release O2 bound
Boston haemoglobin
HisE7 -> TyrE7
= Fe3+
Breaks Fe - HisF8 = Remains T state
HbS
“Gain in function”
β6 Glu -> Val (abnormal hydrophobic interaction)
Polymerisation = distort RBC
Allosteric control
Lactate
Decrease O2 affinity, doesn’t bind to where oxygen binds
Bohr Effect
Increase CO2 and decrease pH
Reduce binding affinity
CO2 - bind to N - terminal
H+ - also protonate ionisable side chains
Stabilise deoxy - Hb
