tetramer, made up of two alpha
subunits and two beta subunits.
each binds a heme
subunit has similar
structure to myoglobin
Myoglobin
made up of alpha helices with connecting
loops with heme sitting in a pocket
Heme contains iron which
can bind to oxygen at one of
its six ligand sites
only unloads oxygen when levels become
unusually low.
Binding of Oxygen
four oxygen molecules bind per
hemoglobin, one per subunit.
binding curve = sigmodial
binding of one oxygen molecule makes it
easier for a second to bind
homotrophic positive cooperative effect =
affinity of binding of oxygen for the fourth
oxygen is 20 fold greater than the affinity for
the first oxygen
Allosteric change
alpha and beta subunit are more
associated with each other than the other
two subunits
when oxgen binds, the subunits change their position. this is due
to the change of shape of heme when oxygen binds.
When oxygen isnt bound iron doesnt fit in the
planar structure but when bound it becomes
smaller and can fit
this change results in the molecule shifting
from low affinity (T) to high affinity (R) state.