M vs H Baseion therom

What does hemoglobin do

It binds O2 cooperatively and allosterically

T/F: all globins bind oxygen, but not all globins are used for O2 transport

true

• The globins use a prosthetic group to do this

What is the prosthetic group of hemoglobin and myoglobin

protoporphyrin

What is omega angle if cis

0 degrees, while if trans it is 180 degrees

What are the ideal phi and psi angles

• phi = -57 degrees

• psi = -47 degrees

The peptide bond exhibits ______, so that all of the atoms associated with the amide bond are ______

resonance, so that all of the atoms associated with the amide bond are planar!

C=0 to N is

omega

apoprotein:

protein without prosthetic group

Holoprotein

protein with prosthetic group bound

What composes the heme group

Porphyrin ring and Fe²+

Porphyrin ring:

• Composed of 4 pyrole rings

• the N of each ring binds to the Fe²+ atom

Heme is planar and binds to a hydrophobic pocket on hemoglobin and myoglobin

• the Fe²+ remains this way if no water (not oxidized to ferric Fe³+)

How does oxygen bind to hemoglobin and myoglobin?

• it double bonds to another oxygen atom on the heme group

• and it also hydrogen bonds to histidine!

  • Far enough to keep iron from being oxidized into being ferric! Need the oxygen to be bound reversibily! The distance is created by the prosthetic group!

• Another histidine (proximal) on the bottom has its nitrogen coordinates to the iron. Prevents iron from oxidizing

T/F: Co and Co2 can bind to the heme group of hemoglobin?

true

• Co (carbon monoxide) binds very tightly essentially irreversibly. It is not displaced by O2. Can cause suffocation.

What is myoglobin

monomer

• Single globin chain!

• Heme binds in a hydrophobic pocket created from 8 alpha-helices

Kd =

[P] [A] / [PA]

Ratio of bound to free protein

[PA] / [P]

P X A reverse arrows P + A

yea

What is P total

[P] + [PA] ==> protien exists between free and bond form.

y =

[A] / Kd + [A] can also think [bound] / [bound] x [unbound]

The more A

the more bound (greater number for fraction of ligand bound)

Mb bound by O2 / total conc of Mb =

Yo2 (fraction of Mb bound by O2)

[MbO2] / [Mb] + [MbO2]

True formula

Y_O2 = [O2] / Kd + [O2]

PO2 / P50 + PO2

P 50

conc of O2 required to bind ½ the myoglobin

What is hemoglobin?

Tetramer: 2 alpha and 2 beta chains

note 4 heme groups (one each in each chain)

What is the monomer and what is the tetramer

monomer: myoglobin

tetramer: hemoglobin

Difference in binding curve between myoglobin and hemoglobin

• Myoglobin has a hyperbolic curve

• Hemoglobin has a sigmoidal curve

  • Binding of O2 is cooperative

  • larger affinity change over a smaller difference in PO2

  • 
    

Allostery:

The capability of one ligand to bind and affect the binding of a second ligand at a distant site

What is positive cooperativity

binding of the first ligand increases the affinity of subsequent ligands

Negative cooperativity

binding of the first ligand decreases the affinity of subsequent ligands.

What does a no cooperativity curve look like?

Standard hyperbolic curve

What does myoglobin do

stores O2 in muscles

• Binds o2 more tightly than hemoglobin

• not quick to release O2

• It releases more slowly to the tissues

What is the Monod, Wyman, Changeauz (MWC) model of allosteric regulation of hemoglobin

• 2 states of the hemoglobin tetramer exist

  • A tense (T) state that does not bind O2 well

  • A relaxed (R) state that bind O2 tightly

what is the tensed state?

where oxygen does not bind well

What is the relaxed state:

binds O2 tightly

In the T state, if O2 binds one of the monomers of the tetramer, it promotes the conformation change of the tetramer to the ______ state, _______ the O2 affinity of the 3 other tetramer

n the T state, if O2 binds one of the monomers of the tetramer, it promotes the conformation change of the tetramer to the ___R___ state, __increase_____ the O2 affinity of the 3 other tetramer

O2 is a ________ effector of HB

homotropic : it affects its own binding by other O2 molecules

Allosteric effector

a small molecule that binds outside of the active site and modulates the activity of a protein

What does 2,3 - BPG do

It stabilizes the T-state. BPG binds better to the T-state than the R-state —> as a result 2,3-BPG stimulates the release of O2

2,3 BPG is a _______ effector

heterotropic: it binds to a regulatory site distant from the active site (not affecting the same molecule)

Where does 2,3 BPG bind

binds to the alpha-beta subunit interface (when in T-state, this space is open, in R state, this space is not open). This is not in the active site!

What does 2,3 BPG do to the curve

makes it more sigmoidal looking! This means that having it present will decrease the affinity of oxygen to the subunits.

What is the Bohr effect

lower affinity of O2 at lower pH releasing O2

• Low pH means hemoglobin does not bind to oxygen as well (less affinity), but myoglobin is unaffected and binds to oxygen normally!

Hydrogen ions and carbon dioxide are also allosteric effectors that can increase the amount of O2 released to the tissues

A higher conc of Co2 and a lower pH (more H+ protons) shifts the curve to the _____, thereby _____ the affinity of hemoglobin for oxygen and allowing it to unload more oxygen to the tissues

shifts curve to the right, decreasing the affinity of hemoglobin for oxygen

When you release a lot of Co2, this ____ the pH

lowers. And this releases more oxygen!