oxygen binding in Hb (2)

T state (tense)

weak binding state

R state (relaxed)

high affinity state

T state affinity

poor

R state affinity

high

state of transition is where what happens?

quaternary shift

alpha beta dimers associate via what 3 interactions ?

hydrophobic

ionic

hydrogen bonds

dimer of alpha beta diners associate via what interactions

ionic and hydrogen bonds

what interactions are disrupted w/pH?

ionic and H bonds

what interactions are disrupted w/pH?

hydrophobic interactions

w/out oxygen bound where is Fe?

out of the heme plane

w/oxygen bound Fe is where and pulls what?

pulled into the heme plane also pulling the His F8 ligand

binding of the first O2 triggers a conformational change (change within the structure of Hb) that allows for?

greater affinity of O2 at other Hb

binding sites within the same molecule

COOPERATVITY of binding multiple O2 molecules results from a

STRUCTURAL CHANGE

T state confirmation

deoxyhemoglobin

R state cofirmation

oxyhemoglobin

what degrees shift during the quaternary shift?

15°

when deoxy-Hb crystals are exposed

to oxygen, they…

shatter, showing evidence of a structural change

one alpha-beta pair moves relative to the other by ___ degrees upon oxygen binding

15

This massive change is induced by

movement of Fe by _______ nm

0.029

T state is stabilized by what that lie at the intersection bw the 2 alpha beta protomers?

ion pairs

Asp-

His+

Oxygen binding initiates a series of movements that result in the

structural shift from the T state to the R state

the movement of T →R affects predominantly the quaternary structure of the

alpha beta protomers

Conformational change occurring as result of trigger-O2 binding to FeII, causing movement of

Helix F

Oxygenation causes

the F helix of one alpha beta dimer to shift relative

to the C-term of the opposite alpha beta dimer

The Fe+2 cannot move toward the heme w/out

reorienting His F8

His F8 is tightly packed in a

hydrophobic pocket and cannot move w/out reprinting Helix F

The translation of Helix F produces

quaternary

shifts

Hb 2 quaternary forms

T or R

1st O2 binding

low affinity T and no cooperatively with p50=30 torr

2nd O2 binding

T→ R and interface destabilized enough for the T→ transition to occur

3rd O2 binding T→ R

cooperatively for 2nd and 3rd O2 (n=2.8 to 3) with p50= 12 torr

4th O2 binding occurs very readily- high affinity R state

high affinity state with p50= 0.3 torr

which binding steps have no cooperativity

1st and last

binding of one O2 at one

site of Hb results in

a strain on the T-state that tears away C-term ion pairs

The result is the quaternary shift in which results in

Hb assuming the R-state conformation, increasing the empty binding sites affinity for O2 = O2 binding being more efficient