Page 48 - The Miracle of the Blood and Heart

THE MIRACLE OF THE
BLOOD AND HEART

As we continue to examine the details of the system, you
shall see that globin's very special shape controls the way iron
binds to oxygen. The four hemes in the hemoglobin molecule
are parallel to one another and vertical to the globin polypep-
tide chains. However, when the heme groups bind oxygen,
this parallel alignment is lost. Even though the hemes are too
far apart to interact direcly, changes that occur in the globin's
structure that surrounds the heme when it picks up an oxygen
molecule are transmitted to the other globins in this protein.
Thus, the act of binding an oxygen molecule at one heme leads
to an increase in the affinity for oxygen binding at the adjacent
hemes.
It should also be noted that the globin keeps pairs of heme
groups from coming too close together, thanks to which, an
oxygen link that might otherwise form among the irons is pre-
vented from doing so. If an oxygen link or "bridge" did form,
then two valuable hemoglobin iron atoms would be oxi-
dized. 24
We may compare this to four separate magnets left hang-
ing from a rod. Since the magnets' north poles are all adjacent,
they will repel one another. If every magnet repels another one
of the same polarity that approaches it, then we encounter a
situation in which all these magnets seek to move away from
one another and thus change their alignment.
When iron ions bind oxygen, they act just like magnets
with the same polarity and try to distance themselves from
each other as far as possible. In our analogy, the "rod" on
which the magnets are suspended is the globin. The threads
by which the magnets hang are the heme groups, and
the magnets themselves are oxygen. The way hemo-
Harun
Yahya

46