The role of carnitine in fatty acid oxidation
Carnitine is a substance that plays an important role in the fat metabolism.
explained in the page about fat metabolism, carnitine is needed to transport the longer fatty acids (C10 and more) into the
mitochondrion where they can be oxidized for energy.Besides
that carnitine also plays an important role in the evacuation of fatty
acids from the mitochondria that cannot be metabolised due to MCAD
activated fatty acid (acyl-CoA) is bound to carnitine to form
acylcarnitine (the CoA is removed). This acylcarnitine can then be transported into the
inside of the mitochondrion using 3 other biochemical processes that
are not further discussed here.
The inside of the mitochondrion is called the matrix.
the acylcarnitine is inside the matrix, the carnitine is released and
the fatty acid is again bound to a CoA. The resulting acyl-CoA can then
be oxidized using beta-oxidation.
The carnitine can leave the matrix and can be bound to the next
acyl-CoA to transport it inside the mitochondrion.
In patients with MCAD deficiency the beta-oxidation is not
(properly) functioning. The medium chain acyl-CoA's can not be further
processed and start to accumulate in the matrix. This substance is
toxic if it remains there in large quantities.
Carnitine plays also an important role in removing these toxic
substances. Carnitine can bind again with them and the resulting
acylcarnitine can be excreted via the kidneys with the urine.
Patients with MCAD deficiency have in their urine (but also in their
blood) a lot of so called octanoylcarnitine. These are acylcarnitines
of length C8
(medium-chains). Also the level of acylcarnitines with lengths C6 and
C10 can be elevated.
carnitine is reused for the transport of other longer fatty acids into
the mitochondria. But in patients with MCAD deficiency a lot of the
carnitine is lost via urinary excretion. So these patients will often
have a shortage of carnitine in their blood.
The carnitine levels in the blood can be restored by taking oral supplements (see the section about treatment for more information).
more about what happens when fasting >