Oxidative Metabolism of Lipids in Liver and Muscle - Study Notes

Steps of β-Oxidation with Enzymes

  • Overview of Four Main Steps:

  1. Acyl-CoA Dehydrogenase: Forms double bond between carbons and requires FAD.

  2. Enoyl-CoA Hydratase: Adds water to the double bond, forming an alcohol.

  3. Hydroxyacyl-CoA Dehydrogenase: Converts the alcohol to a ketone and requires NAD+.

  4. Thiolase: Cleaves the fatty acid chain, releasing acetyl-CoA and a shorter fatty acyl-CoA.

Coenzymes Associated with β-Oxidation Enzymes

  • Enzymes and Their Coenzymes:

  1. Acyl-CoA Dehydrogenase: Requires FAD.

  2. Enoyl-CoA Hydratase: H2O

  3. Hydroxyacyl-CoA Dehydrogenase: Requires NAD+.

  4. Thiolase: CoASH

Tissues That Utilize Ketones

  • Skeletal & Heart muscles

    • Source of energy ( requires Succinyl-CoA and CoA)

  • Brain

    • 50% of energy ( only during starvation)

Transport of Fatty Acids to Mitochondria

  • Short Chain fatty acids: Free diffusion @ mitochondrion

  • Medium-chain Fatty Acids: Diffusion @mitochondrion

  • Long chain Fatty Acids: Carnitine Cycle @mitochondrion

  • Very Long-chain Fatty Acids:Unknown @peroxisome

Carnitine Shuttle Mechanism

  • Components:

  • CPT1 :

    • Located on the outer mitochondrial membrane, I

    • Converts Long chain FA —> Carnitine

  • CPT2

    • Recycles Carnitine

    • Transfer fatty acyl CoA —> mitochondrial matrix

  • Composition: Carnitine is derived from the amino acids lysine and methionine. It is often synthesized in the liver and kidneys.