In another set of these
lectures, I've talked about the
importance of heme for carrying
oxygen within hemoglobin.
In these set of lectures, I'll
talk about how that heme is made
and how the iron in the heme is
transported and stored in the body.
Now, heme is as you've seen in the other
lectures, a flat, planar structure
that contains a porphyrin ring with
an atom of iron at its very center.
The ring structures that hold the iron
can serve as a sink for electrons
and this can be valuable also for
the process of electron transport.
The ring also enables
the carrying of oxygen
which is what happens
inside of hemoglobin.
So, hemes are usually found
attached to proteins.
That's true whether they're
in the electron transport
system or they're contain within
a hemoglobin or myoglobin.
The examples, of course, include
these proteins: hemoglobin,
myoglobin and the cytochromes of
the electron transport system.
The names of the cytochromes in
the electron transport system
come from the hemes
that they contain.
Cytochrome a, for example
contains heme a.
The ring structure that's found
in the hemes of hemoglobin,
myoglobin and cytochromes is
also found in the chlorophyll.
And in the chlorophyll, the ion is
replaced with the magnesium at its center.
The cobalamins, also known as
vitamin B12, have a cobalt
at their center instead
and we can see that here.
Now, the structure and function of hemes
is related to their planar structure.
And we can see that the various
hemes have a very similar central
structure as we see in Heme A,
Heme B , Heme C and Heme D.
And we see that the primary differences
of these different forms of heme
are due to alterations on the
outer part of the molecule.
These have little effect on the function
of each of the individual hemes.
Heme A is found as part of the
complex IV of the electron
transport system and it’s the
part where oxygen is reduced.
Heme B is the most common type that
we see and it's found in hemoglobin,
myoglobin, peroxidase enzymes and cycloxygenase
enzymes for making prostiglandins.
Other proteins that contain heme B include
the P450 hydroxylation system of the liver
and the nitric oxide synthase system that
we've talked about in other lectures.
Now heme C is found as the name
would suggest in cytochromes C,
a very important protein in the
electron transport system.
And it links to the protein via
cysteines, the sulfur side chains.
Heme O functions in bacterial
oxygen reduction very much
like the heme A does where the
complex IV reduces oxygen.