The next family of amino
acids whose metabolism
we will consider is that
of the pyruvate family.
Now, pyruvate metabolism is tied very
closely to the amino acid alanine.
And we see again transamination appearing
as a very important consideration.
Transamination of pyruvate is what
leads to the production of alanine.
The donor in this case
of the amine group is
glutamate as we've seen
for other reactions.
And the enzyme involved in
this is alanine transaminase.
We can see that, of course, the amine comes
from glutamate, goes on to make alanine.
is what makes the
alpha-ketoglutarate on what
was originally glutamate.
Alanine is a byproduct of the catabolism
of valine, leucine and isoleucine as well.
So, break down of those amino acids is
an alternate way of making alanine.
Alanine is a very important molecule for
managing the movement of amines in the body.
This occurs as a result
of the glucose-amine --
I'm sorry, the glucose-alanine
cycle which I will show here.
So, the glucose-alanine cycle
overlaps with the cori cycle.
And they are both shown
in this figure right here.
The cori cycle on the right and the
glucose-alanine cycle on the left.
They have in common the features
that are shown in the center.
So to describe these pathways,
I want to show a little bit about what's
happening in the individual conditions.
If we start in the bloodstream with the
glucose, glucose goes to tissues that need it.
I've picked muscle here as an example, but
we could be talking about brain as well.
When cells are breaking down glucose
and there's a lack of oxygen,
they will go in this
cycle to the right.
Now, that's important in rapidly
metabolizing muscles tissue for example.
And these circumstances, ammonia
concentration is probably fairly low.
When that happens,
pyruvate is converted into
lactate because the oxygen
is commonly limiting.
Lactate is taken from those
tissues and moved back
to the bloodstream and
ultimately to the liver
where it is converted back to pyruvate
and then ultimately made back
into glucose for additional energy
for those tissues that need it.
Other conditions where we have high ammonia
however, a different circumstance happens.
Now this might happen in muscle.
It might more commonly
happen in brain
because is very sensitive to the high
ammonia levels that can be produced.
So if that happens, pyruvate is converted
into alanine by a transamination reaction.
That movement of that amine out of
the brain is very, very important.
That transaminaton that
I've just showed is the
one that's most commonly
done to produce this.
Alanine produced in this way
is dumped into the bloodstream
and alanine is then taken to the liver
where it's converted back to pyruvate
and that amine group is
converted ultimately into urea.
Now, this turns out to be
important because glutamate,
which is a way of mopping
up that amine group
that I've talked about,
is a neurotransmitter.
So for talking about the brain,
we really don't want to be moving that
neurotransmitter out of the brain.
Putting it on to alanine
and letting alanine carry
it to the liver is a more
So having alanine carry
the amine is a very, very
important part of the
The transamination in the liver
now is removing the amine
and that amine then is
put on to making urea,
and urea is the way that we
excrete that excess amine.
Breakdown a glutamate therefore
yields amine for a urea production.