Now, nitrogen compounds are
very important for making amino
acids and all the other molecules
that I've talked about.
But there are some very hazardous
components of nitrogen
metabolism that I need to discuss
and we need to understand.
These components I'll describe
in the next couple of slides.
And the first of these involves a fairly
reactive molecule known as nitrites.
Nitrites appear in our food and our
made in our body from nitrites.
So let's see what happens with them.
Nitrite can be formed by the
ionization of nitrous acid, HNO2,
or by the reduction of nitrites.
Nitrite is used to cure meats.
Bacon for example is a preserved
by treating it with nitrite.
This is done to prevent botulism and
it’s an acceptable use of nitrite.
When it’s reduced to nitric oxide,
it happens in hypoxic conditions.
Production of nitric oxide is good
if the cell is trying to signal
it and it is bad if the cell is
not trying to use to signal it.
In the human diet, the most common source
of nitrites is not from consuming them
in meats but rather from the reduction
of nitrites that appear in vegetables.
And how did the nitrites
get in to the vegetables?
Well, two ways.
One by fertilizer and
one by plant stress.
The hazards with nitrites
are associated with its
ability to form cancer
This happens in acidic conditions
such as we have in our stomach.
Nitrites can oxidize
and convert it from a plus
two form, the ferrous
form to a plus three
form the ferric form.
Well, when that happens within hemoglobin,
that hemoglobin is nonfunctional.
It will no longer be
able to carry oxygen.
So, consumption of a lot
of nitrites or creation of
a lot of nitrites can be
a very serious problem.
So nitrosamines are produced from
nitrites by a couple of reactions that I'm
going to show you here that involve
water, acid and secondary amines.
So, here’s the reaction process.
A nitrite that's in our
body is shown on the left
there or actually in the
center of the slide.
In an acid environment as indicated
by the two protons there,
nitrous acid ion
is created H2NO2+
and that will spontaneously come apart
to form water and nitrosonium ion.
The nitrosonium ion in
the next step of the
process combines with the
secondary amines such
as proline and that
produces the very hazardous
nitrosamine that you
can see on the right.
Now nitrosamines, because the R groups
are there, are classes of compounds.
It’s not one structure because
those R-groups can have
various [INAUDIBLE 00:02:40]
associated with them.
Strong acids, as
we've seen here,
are high temperatures such as frying
favor the production of nitrites.
These compounds, as I said,
are found in processed meats.
They are also found in beer.
They're found in cigarette
smoke and in chewing tobacco.
The formation of nitrosamines is actually
inhibited by vitamin C and is on reason that
people think vitamin C is something that has
a very protective mechanism for our body.
Now, nitrosamines are problems
in the body because they
can react with DNA to form
what are called DNA adducts.
In these reactions, nitrosamines are
covalently joined to basis of DNA.
In joining those bases to the
DNA, means that when the DNA
has copied, it's much more
likely to form a mutation.
Well, this means that nitrosamines
are very likely carcinogens.
Meaning they cause
cancer in humans.
And there is pretty good
evidence that nitrosamines are
associated with gastric and
esophageal risks of cancer.
Now, how do we get
nitrosamines in other ways?
Well, a very good way of
getting them besides the
way that I’ve described so
far is through tobacco.
Nicotine and its
metabolites that are made
from it can form
nitrosamines quite readily.
One nitrosamine called
NNK is nicotine derived
and it is very important
We can see NNK in the figure on
the right part of the screen.
NNK is found in tobacco and it's
also found in e-cigarettes.
So you don't escape it
by smoking e-cigarettes.
NNK activation by P-450
system of your liver
is important in activating signaling
cascades and uncontrolled growth.
And we've seen in other
lectures how losing
control of signaling
cascades is a big problem.