Test 2: Hemoglobin and Myoglobin Flashcards
where is myoglobin located
in muscles
where is hemoglobin located
in red blood cells
describe the Hb subunits
4 subunits that are homologous to MB
which structure was the 1st one discovered by x ray cyrstallography
myoglobin
how man helices does myglobin have
8 alpha helices labeled a through H
what are the differences between myoglobin and hemoglobin
- myoglobin is a monomer, Hb is a tetromer of 4 Mb like homo subunits
describe the Hb subinits
2 alpha globin and 2 beta globin
who solved Hb structure
Max perutz
what is heme
protoporphyrin IX + Fe+2 + Mb
- in Hb each subinits has a heme proesthetic group
what does it mean by prosthetic group
it means the non amino acid portion of a protein that is required
what does the heme group do in hemoglobin
in each of the 4 subinits it binds oxygen in the lungs and releases it in tissues
what does the heme group do in Mb
stores and releases oxygen for muscle activity
what does the Fe+2 do in the heme
responsible for binding to oxygen and it switches between different oxidation states
what doe His E7 do the binding pcoket of heme
- forces any ligand to bind to Fe(II) at a bent angle
- bent allows for O2 ot bind FE(II) on heme reversibily
what is holding the heme in place
hydrophobic interactions
what bond is holding the heme in place to each Hb subinits/ Mb in proximal His
coordinate covalent bond to His F8
which His is directly binded to the Iron
His F8 proximal
what does His 8 do
- bonded to iron
- anchor iron
- positions the heme group
what is the role of His E7
- does not directly bind to the iron
-stabilzie O2 molecule - reduces harmul molecules like CO
- binds O2 bent to stabilize it
pls describe CO poisioning
- CO has a strong affinity for Fe+2 and when binded linerly and it prefers linear binding it is 20,000 stronger than O2
- but steric hinderance of His e7 reduces the effect
why is CO, CN, NH3, NO, and H2S bad
bind in place of ocygen on a heme in complex IV of ETC
what happens when the O2 gets oxidized to FE+3 in Hb and Mb
- ## gives Methemoglobin ( brown)
what is important about MetHB and MetMB when binding
- they can’t bind O2
what enzyme can reduce Fe+3 to Fe+2
diaphorase
how can Fe+3 be formed
- 2 hemes w/out a protein come and autoxidize through intermediate ( O2 bridge between two Fe(II) centers)
what prevents FE+3 from being formed
- bulky groups around heme
what is the Mb O2 binding eqiation
Mb+ O2 = MbO2
what is the equation for the fraction of Mb bound to O2
Y = O2/ O2= Kd
what is Kd in the Mb fraction equation
Kd is the dissociation constant
affnity of Mb for oxygen
low Kd means what and High kd means what
low kd = higher affinity
high Kd= lower affinity
what curve does Myoglobin show
hyperbolic curvewhat
what is the 1/2 saturaiton of Mb
p50( 1/2 sat ) = 2.8 torr
does Mb give a lot or less O2
little O2 over a normal physiolgogical range
what happens with O2 in Mb during exercise
- O2 doesnt transport fast enough
- PO2 falls low allowing Mb to release O2
- YO2 drops from 0.97 to 0.91
what does each Hb subinit have
heme and O2 binding site
why does Hb transport O2 from lungs to tissues
because O2 diffusion in larger animals is poor so they need Hb to do it
what is the structure of Hb
dimer of 2 alpha and 2 beta
(ab)^2 dimer
what happens when O2 binds to Hb
there is a conformational change in the quaternary strucrure and Mb does not have this
what are the 2 states of Hb
deoxy- tense T state
oxy - R state (relaxed)
what does the switch between states invovle
15o twist
- rotation between ab dimer pairs
describe the affinity for T and R state
- T = low O2 affinity
- R = high O2 affinity
how does O2 binding Hb effect T to R state switch
- communication cannot be electronic bc hemes are too far apart
what AA is present in T state
lys 82
what is the structural change that happens during T state
- heme groups are slightly distored bc iron is pulled out of the plane
- 4 subinits are more tight together
structural change in R state
- o2 pulls the iron INTO the plane
- salt bridges are broken allowing the subunit units to move freely
why is iron pulled out of the plane in the porphyrin ring
iron is in a high spin state making it too large to fit within the plane
why is iron pulled into the plane for R state
- change int he iros electronic congiruation, reducing its size and allows it to move in
how does His f8 move in T and R
- T pulls slugly downward
R- pulls it along with it caues a domino effect causing a shift in th eentire protein structure
what bonds are present in T state
- H bonds and ion pairs (Not present in R state)
why is it difficult for T to bind the 1st O2
His E7 and Val E11 block access to heme
- HIs E7 is connected to the iron and t is at bent angle
how many angstroms is FE+2 out in T state
0.6
what happens when the 1st O2 binds
pulls FE+2 back itno the heme plane wich is R state
what does His F8 pull
the F helix like a lever and then it movesw
what happens when F helix moves
ab pairs rotate with respect to each other meaning a change in the Quat structure of Hb
what happens in the A1-b2 and a2-b2 binding
equivalent h bonds and ion pair act like knobs
when we are shiftig between T to R what happens to His e7 and val e11
move out of the way so theo2 has more access to the heme
where does the energy to breka the ion pairs and H bonds in the t state come from
the energy in the formation of Fe-o2 bond formation drives the transition from T to R
what mechanism did we jsut describe
the perutz mechanism
Hb in r state has what curveq
sigmoidal because we have +ve cooperativity ( Rstate and T state binding curve)
what is positive cooperativity
binding of a molecule increases the likelihood that additional molecules will bind to other binding sites
pls expain the + cooperativity
- low affinity T state o2 can’t bind
2. 1st o2 binds to one of the 4 subunits caues the ionic = hbonds to disrupt - transition to R state due to the hemoglobin to move in and causes the other subinits to bind
4. the curve is then sigmoidal
whyis Hb an ideal O2 transport protein
S shaped YO2 curvew
what is the p50 for Hb
26 torr
in lungs what does the p02 =
100 torr
