key changes in hemoglobin as it transitions from the T state to the R state upon the binding of oxygen

upon O₂ binding, porphyrin ring goes

from puckered to flat

results in a shift in the

position of proximal His

shift in position of

alpha helix bound to proximal His

shifts in

the entire subunit

disruption of salt bridges in the T state as a result of

His at C-term of beta subunit moving toward the center

gap between beta subunits

narrows and Hb relaxes into R state