Alpha Oxidation of Fatty Acids

Table of Contents

• What are Fatty Acids?
• Types of Oxidation in Fatty Acids
• Steps of Alpha Oxidation
• Significance of Alpha Oxidation
• Clinical Significance
• Frequently Asked Questions

What are Fatty Acids?

Fatty acids are carboxylic acids that possess aliphatic chains that can either be saturated or unsaturated. Most fatty acids are naturally occurring, unbranched and possess an even number of carbon atoms. Fatty acids are an important dietary source and also function as structural components of cells.

Types of Oxidation in Fatty Acids

• Beta oxidation: It is the major mechanism of oxidation of fatty acids that occurs in mitochondria and peroxisomes. It releases acetyl CoA by breaking the carbon chain between C2 and C3.
• Alpha oxidation: It is a minor oxidation pathway that occurs in peroxisomes. The chain is broken between C1 and C2 and releases CO₂ per cycle.
• Omega oxidation: It is another minor oxidation pathway that occurs in the endoplasmic reticulum. The action site for this type of reaction is the methyl end of the molecule.

Steps of Alpha Oxidation

The phytanic acid, a branched-chain fatty acid that is obtained in humans by the fat of ruminant animals, dairy products and plant materials, is the primary target for alpha oxidation. Plant materials contain chlorophyll that releases phytanic acid in humans. The steps of alpha oxidation of phytanic acid are as follows:

• Phytanic acid first attaches with CoA to form phytanoyl-CoA.
• The phytanoyl-CoA is oxidised to 2-hydroxy phytanoyl-CoA in the presence of phytanoyl-CoA dioxygenase using Fe²⁺ and O₂.
• 2-hydroxy phytanoyl-CoA is cleaved to form pristanal and formyl-CoA in the presence of 2-hydroxyphytanoyl-CoA lyase.
• Pristanal undergoes oxidation to form pristanic acid in the presence of aldehyde dehydrogenase. The pristanic acid can then undergo beta oxidation.

Significance of Alpha Oxidation

• Alpha oxidation yields simpler forms of fatty acids that can later undergo beta oxidation. For example – beta oxidation cannot occur in phytanic acids because of the presence of a β-methyl group. Alpha oxidation removes the methyl group by decarboxylation, and hence beta oxidation can proceed.
• It produces intermediate hydroxy fatty acids such as cerebronic acid that can be used to synthesise cerebrosides and sulfatides.
• The decarboxylation of fatty acids produces odd chain fatty acids that can be used in the synthesis of sphingolipids.

Clinical Significance

Refsum disease is caused by the deficiency of the enzyme phytanoyl CoA 2-hydroxylase. This leads to impairment in the alpha oxidation pathway of the phytanic acid. As a result, phytanic acid is accumulated in cells and tissues. It is presented by symptoms such as neurological damage, peripheral neuropathy and cerebral degeneration. Symptoms include ataxia, night blindness, cataracts, scaly skin and difficulty in hearing.

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Related Links:

• What are Lipids? – Definition, Structure & Classification of Lipids
• Importance of Fats – Types of Fats, Sources and Its Benefits