Fatty acid β-oxidation is the process by which fatty acids are broken down to produce energy. Fatty acids primarily enter a cell via fatty acid protein transporters on the cell surface. Once inside, FACS adds a CoA group to the fatty acid. CPT1 then converts the long-chain acyl-CoA to long-chain acylcarnitine.
3. BETA OXIDATION
Beta oxidation may be defined as the oxidation of fatty acids on
the beta carbon atom.
More specifically, beta oxidation consists in breaking down
long fatty acids that have been converted to acyl-CoA chains into
progressively smaller fatty acyl-CoA chains.
Beta oxidation goes on until two acetyl-CoA molecules are
produced and the acyl-CoA chain has been completely broken
down.
In eukaryotic cells, beta oxidation takes place in the mitochondria,
whereas in prokaryotic cells, it happens in the cytosol.
4. Activation of fatty acids- in the cytosol
Transport of fatty acids into mitochondria.
Beta-Oxidation in the mitochondrial matrix [fatty
acids are oxidised by most of the tissues in the
body].
Brain, erythrocytes and adrenal medulla cannot
utilise fatty acids for energy requirement.
steps
5. *
*Fatty acid activation takes places in the cytoplasm.
*Fatty acids are activated to acyl CoA by thiokinases
or acyl CoA synthetases.
*This reaction occurs in 2 steps and requires ATP,
coenzymes A and Mg2+.
*Fatty acid reacts with ATP to form acyladenylate
which then combines with coenzymes to produce
acyl CoA.
*Two high energy phosphates are utilized, as ATP is
converted to pyrophosphate[PPi].
6. The inner mitiochondrial membrane is
impermeable to fatty acids.A specialized
carnitine carrier system [carnitine shuttle]
operates to transport activated fatty acids
from cytosol to the mitochondria.
Transport occurs in 4 stages
Acyl group of acyl CoA is transfrred to
carnitine catalysed by carnitine
acyltransferase1 [CAT-1], present on the
outer surface of the inner mitochondral
membrane.
7. The acyl-carnitine is transported
across the membrane to mitochondrial
matrix by a specific carrier protein
[Translocase].
Carnitine acyltransferase-2 [CAT-2],
Found on the inner mitichondrial
membrane, which converts acyl-
carnitine to acyl CoA.
The carnitine released returns to
cytosol for reuse by translocase.
8. Each cycle of beta oxidation, liberating a two
carbon unit-acetyl CoA, occurs in a sequence
of four reaction
1.OXIDATION
Acyl CoA undergoes dehydrogenation by an FAD-
dependent flavoenzyme, acyl CoA dehydrogenase.
A double bond is formed between alpha and beta
carbon [ 2 and 3 carbon]
2,HYDRATION
Enoyl CoA hydratase brings about the hydration
of the double bond to form beta hydroxyacyl CoA.
*
9. 3.OXIDATION
*Beta- hydroxylacyl CoA dehydrogenase catalyses
the second oxidation and generates NADH. The
product formed is beta-ketoacyl CoA.
4.CLEVAGE
*The final step is the liberation of a 2 carbon
fragment, acetyl CoA from acyl CoA,
*This occurs by a thiolytic cleavage cataysed by
beta ketoacyl CoA thiolase or thiolase.
*The new acyl CoA, containing two carbons less
than the original, reenters the beta oxidation cycle.
The process continues till the fatty acid is
completely oxidised,
