Now zymogens come in many forms and
synthesizes zymogens for many reasons.
On the last slide, I showed
some of the individual zymogens that are proteases
and there are actually quite a few proteases
that are synthesized in an
inactive form; because, proteases
are pretty strong and can cause some big problems.
But not all of them are, in fact, involved in digestion.
One group of those it’s very interesting are those that are
blood clotting proteins that you can see near the bottom.
Blood clotting is a process that's controlled by
a cascading system like I described
and that cascading system
starts with a simple action.
That is then amplify through many steps
and that amplification causes
ultimately the formation of a clot.
Well, to make enough proteins
sufficient to clot blood
and organize them and do that
before the person dies of bleeding.
That takes quick action and that's why that
cascading affect that I mentioned is really important.
Another group of proteins that are synthesized as
zymogens in the inactive form are shown on the right.
And the second of those is
also interesting because
it's involved in catalyzing the reversal of the
process of clotting, that is un-clotting of blood.
One could imagine the important of managing that
because you don't want to start dissolving a clot
until the tissue has repaired itself or else you
are gonna start the bleeding process again.
So the synthesis of plasmin in an
in active form as plasminogen
allows the body to manage when that clot would
be dissolved and how it would be dissolved.
Now there are also chemical
modifications that affect
enzymatic activity. In some of the other
presentations you have seen some of those.
Those included phosphorylation
of the enzymes in glycolysis
and acetylation of histones that
happened in the chromatin of DNA.
The other modifications are quite varied
and have multiple affects
on enzymes and other proteins.
Some of those affects can activate those and
some of those affects can inactive those.
The very last one is another one I wanna
mention about clotting proteins; because,
it brings up yet another point about
the importance of these changes.
Now the regulation of the last blood clotting
protein is a very interesting one; because,
it's chemical modification doesn't change the
enzyme from an inactive form to an active form.
The protein involved in this
called prothrombin and though
it doesn't sound like it's a zymogen, it
is, because it has an older nomenclature.
Prothrombin is an inactive form of a
protease that is necessary to clot blood.
Now that protease like other
proteases has to be a controlled.
But what you see on the screen happening is
not the control of the catalytic activity.
But the control of where
the enzyme will end up.
So in this case we see the side chain of one of the
amino acids of prothrombin known as glutamate.
In the reaction that you see on the
screen, the glutamate gains an extra carbon dioxide
and that extra carbon dioxide gives the side
chain an interesting property.
The interesting property is that with the
extra carboxyl group it can bind to calcium.
Now calcium is present more at the
side of the wound than it is elsewhere.
The modification of prothrombin in this way
puts this inactive form of the enzyme
close to the side of the wound
so it can be activated very readily to
help the clotting process happen.
And this is one of the steps in that
cascading mechanism that I talked about.