What is the alpha oxidation of fatty acids?

Alpha oxidation occurs only im peroxisomes. And used for oxidation of Branched‐chain fatty acids as Phytanic acid.

The concept is that Branched‐chain fatty acids can't be oxidized directly by β‐oxidation, becouse they have at β‐carbon position methyl group, that do not permit to oxidize this b-carbon. Exactly becouse of branched methyl group they are called branched chain FA’s. So the goal here is to make b-carbon position free. And peroxisomes solve this problem by Peroxisomal alpha oxidation, simply by making b carbon - α–carbon.

For more detailed explanation you can watch - 0: 50

• Oxidation of Fatty acid

Fatty acid oxidation is the mitochondrial aerobic process of breakdown of fatty acid to form a acetyl-CO.A units.

There are several types of fatty acids oxidation.

1. Alpha-oxidation of Fatty acid
2. Beta-oxidation of Fatty acid
3. Omega-oxidation of Fatty acid

But of these, the highest beta-oxidation is found in organisms.

• Beta-oxidation of Fatty acid

Beta-oxidation is the catabolic process (breaking down) by which fatty acid molecules are broken down in the cytosol in prokaryotes and in the mitochondria in eukaryotes to generate acetyl-CO.A. After production acetyl CO.A is fed directly into the Kreb's Cycle or Citric acid cycle and NADH and FADH2, which are co-enzymes used in the Electron Transport Chain (ETC).

It's occurs in many tissues including liver, heart, adipose tissue and kidney.

Oxidation of fatty acids doesn't occur in the brain.

• The beta-oxidation of fatty acids involve three stages:-

I. Activation of FA (fatty acids) in the cytosol.

II. Transport of activated FA into mitochondria.

III. Beta-oxidation proper in the mitochondrial matrix.

I. Activation of FA (fatty acids) in the cytosol.

This reaction is catalyzed by acyl CO.A synthetase present in cytosol. This enzyme requires ATP, COASH, magnesium ion. The product of this reaction is fatty acid acyl CO.A and water.

II. Transport of activated FA into mitochondria

Transport of fatty acid acyl CO.A from cytosol into mitochondria with the help of special transport mechanism called Carnitine Shuttle.

III. Beta-oxidation proper in the mitochondrial matrix.

There are four steps in beta-oxidation.

Step-I Oxidation by FAD linked Dehydrogenase enzyme.

Step-II Hydration by Hydratase enzyme

Step-III Oxidation by NAD linked Dehydrogenase enzyme

Step-IV Thiolytic cleavage by Thiolase enzyme

• The first reaction is the oxidation of acyl CO.A. In this reaction acyl CO.A is converted into alpha-beta unsaturated acyl CO.A. This reaction is catalyzed by acetyl CO.A Dehydrogenase. FAD is the hydrogen acceptor.
• The second reaction is the hydration. In this reaction alpha-beta unsaturated acyl CO.A is converted into beta-hydroxy acyl CO.A. This reaction is catalyzed by alpha-beta unsaturated acyl CO.A Hydratase.
• The third reaction is the oxidation of beta- hydroxy acyl CO.A is converted into beta-keto acyl CO.A a NAD- dependent reaction. This reaction is catalyzed by beta-hydroxy acyl CO.A Dehydrogenase.
• The fourth reaction is Thiolytic cleavage of the two carbon fragment by splitting the bond between alpha and beta carbons. By Thiolase enzyme.
• The release of acetyl CO.A leaves an acyl CO.A molecule reduce by 2 carbons.
• This acyl CO.A molecule is the substrate for the next round of Oxidation starting with acyl CO.A Dehydrogenase.
• This process repeats until the original fatty acyl CO.A turns into an acetyl CO.A.
• In the last round a 4 carbon acyl CO.A is cleaved to 2 acetyl CO.A.
• Example - Beta-oxidation in Palmitic Acid (16C)