Oxidation of unsaturated fatty acids presents a challenge due to the cis-double bonds they possess.
Beta oxidation involves intermediates with trans-double bonds.
Specific enzymes are required to process unsaturated fatty acids.
Key Enzymes Involved
Enoyl-CoA Isomerase
Converts cis 3,4 double bonds to trans 2,3 double bonds.
Trans 2,3 double bond is a normal intermediate in beta oxidation.
2,4 Dienoyl-CoA Reductase
Utilizes electrons to convert two double bonds into one double bond.
The resulting double bond is then converted by Enoyl-CoA isomerase.
Metabolism of Long Chain Fatty Acids
Fatty acids with chain lengths of 20-22 carbons or greater are metabolized differently.
Initial oxidation begins in the peroxisome, not in the mitochondria.
Odd-Numbered Fatty Acids
Fatty acids with odd numbers of carbons are processed differently due to the resultant 3-carbon propionyl-CoA.
Propionyl-CoA Carboxylase adds a carboxyl group to form methylmalonyl-CoA.
Methylmalonyl-CoA Mutase (requires vitamin B12) rearranges the molecule to form succinyl-CoA.
Succinyl-CoA enters the citric acid cycle for further metabolism.
Energy Production
Each round of fatty acid oxidation produces:
1 molecule of FADH2
1 molecule of NADH
1 molecule of acetyl-CoA
Fatty acids are shortened by two carbons with each cycle.
Acetyl-CoA enters the citric acid cycle within the mitochondria.
Importance of Vitamin B12
Essential for the activity of methylmalonyl-CoA mutase.
Deficiency can impair fatty acid metabolism.
Summary
The lecture by Kevin Ahern, PhD, provides detailed insights into the mechanisms of fatty acid oxidation, especially focusing on unsaturated and long chain variants.
Understanding these processes is crucial for appreciating how cells manage energy production from fats.