Well, it turns out that there’s
yet another molecule that
plays an important role in the
process of release of oxygen.
The molecule is what
you see on the screen.
It’s 2,3 BPG or 2,3
This molecule is a byproduct of the process
of glycolysis, the breakdown of sugar.
And it’s a relatively
It’s not made in the individual
reactions of glycolysis,
but as a byproduct in the synthesis
of one of the molecules.
That’s not really important.
But what is important is that
it’s made at a low level
when cells are going through
metabolism of glucose.
If you’re exercising heavily, like you
might be in the race or the marathon run,
then you’re more likely be
producing more of this 2,3 BPG
than if you’re sitting around eating pizza,
drinking beer and watching television.
tissues produce acid.
They produce carbon dioxide
and they produce 2,3 BPG.
Now this molecule works in a little
bit different way than the other two.
It works by binding in the hole
of the donut of hemoglobin.
So when we look at the
structure of hemoglobin,
the very center of it,
there’s a cavity.
There’s nothing in that cavity.
And it turns out that’s
exactly where 2,3 BPG binds.
What 2,3 BPG does is when
it binds in that cavity,
it converts and stabilizes
hemoglobin in T-state.
Now the T-state you may remember is the
state that does not like to have oxygen.
So by 2,3 BPG binding into
the whole of the hemoglobin,
it’s favoring hemoglobin getting
rid of as much oxygen as it can.
So here’s a third signal that it’s a rapidly metabolizing cell,
that the hemoglobin needs to let
go of its oxygen and it does that.
If we measure the same
curves that we saw before,
now changing the pH, the
concentration of 2,3 BPG
and the concentration of carbon
dioxide, the more the pH falls,
the more 2,3 BPG is added, and the
more the carbon dioxide increases,
the more the curves move to the right
favoring the release of oxygen.
So rapidly metabolizing
cells produce acid.
Rapidly metabolizing cells
release carbon dioxide.
And rapidly metabolizing
cells release 2,3 BPG.
All these favor oxygen
release form hemoglobin.
So rapidly metabolizing cells get the
oxygen they need as much as possible.
Now 2,3 BPG is interesting
in another perspective.
If we think about hemoglobin
bound to that 2,3 BPG,
the 2,3 BPG in the hole of hemoglobin,
we see hemoglobin in the T-state.
And you might wonder what
happens if hemoglobin gets back
to the lungs with that 2,3 BPG
stuck in the middle of it.
Because the 2,3 BPG
favors the T-state,
it’s less likely that the hemoglobin
is going to bind to oxygen.
Well, normally, in the course of
things, as hemoglobin is exiting
the tissues that it is in, hemoglobin
will let go of the 2,3 BPG.
2,3 BPG is grabbed by the cells that
this hemoglobin is passing through
in the blood system, and the cells
grab the 2,3 BPG and use it.
So the normal course of things,
hemoglobin gets back to the lungs
and it’s lost its 2,3 BPG.
That’s not true for smokers.
Smokers have a lot of 2,3 BPG in their
blood much more than nonsmokers.
So what happens is if hemoglobin
lets go of its 2,3 BPG,
and the blood of a smoker,
there’s more 2,3 BPG
present to go back and
find the hemoglobin.
That makes it much more likely
that 2,3 BPG will be bound
to hemoglobin when the hemoglobin
gets back to the lungs.
This locks hemoglobin in the T-state when it’s in the lungs
and the oxygen carrying capacity of
hemoglobin in the lungs is reduced
because more of it is in the
T-state in the blood of a smoker.
Now another side effect of
that happens with smokers
is very important to
understand with respect to
hemoglobin is that smokers
oftentimes have a higher
concentration of carbon
monoxide in their blood.
It comes from the smoking
of the cigarettes.
Carbon monoxide looks to hemoglobin
an awful lot like oxygen.
And the reason carbon monoxide is poisonous,
one of the reasons it’s poisonous,
is because it competes with oxygen for
binding to the iron on hemoglobin.
So the smokers losing
on two accounts.
They’re losing on the
carrying capacity of
oxygen by hemoglobin
because of the 2,3 BPG,
and for the hemoglobin that
has no 2,3 BPG is much more
likely that it will have
carbon monoxide at that point.