Beta oxidation

β-Oxidation of Fatty Acids

Types of Fatty Acids

  • Saturated Fatty Acids (FAs)
    • Even number Carbon FAs
    • Odd number Carbon FAs
    • Found in lipids of plants and some marine organisms.
    • Many ruminant animals form a large amount of 3-carbon propionate during carbohydrate fermentation in the rumen.
  • Unsaturated Fatty Acids
    • Monounsaturated
    • Polyunsaturated

Mobilization of Stored Fat

  • Fatty acids (FAs) are released from their triacylglycerol (TAG) form by hormone-sensitive lipase.
    • Glycerol is the other product formed.
    • The enzyme removes a FA from either C1 or C3 of the TAG.
  • Remaining FAs are removed by specific lipases.
  • Hormone-sensitive lipase is activated by a 3',5'-cyclic AMP dependent protein kinase.
  • 3',5'-cAMP is produced in the adipocyte when hormones such as epinephrine (norepinephrine), glucagon, and adrenocorticotropin bind to cell membrane receptors, activating adenylate cyclase.

Mobilization of Triacylglycerols

  • Low glucose levels trigger hormone release, leading to the following sequence:
    1. Hormone binds its receptor in the adipocyte membrane.
    2. Stimulation of adenylyl cyclase to produce cAMP.
    3. Activation of PKA (protein kinase A).
    4. Phosphorylation of both hormone-sensitive lipase and perilipin molecules on the lipid droplet's surface.
    5. Phosphorylation of perilipin allows hormone-sensitive lipase access to the lipid droplet.
    6. Hormone-sensitive lipase hydrolyzes triacylglycerols to free fatty acids.
    7. Fatty acids exit the adipocyte, bind to serum albumin in the blood, and are transported.
    8. Fatty acids are released from albumin and enter myocytes via a specific fatty acid transporter.
    9. β-Oxidation follows, generating FADH2, NADH, and Acetyl CoA, leading to the T