Transport and oxidation
The neutral lipids stored in adipocytes (and in steroid synthesizing cells of the adrenal cortex , ovary, and testes) in the form of lipid droplets, with a coreof sterol esters and triacylglycerols surrounded by a monolayer of phospholipids are coated with Perilipin, a protein that acts as a protective coating from the body’s natural lipases, such ashormone-sensitive lipase,. However, when a hormone such as epinepherine and glucagon are secreted in response to low levels of glucose, this triggers an intracellular secondary messenger cascade thatphosphorylates hormone-sensitive lipase to break triglycerides into glycerol and free fatty acids for use in metabolism, a process called lipolysis.
The free fatty acids move into the blood stream wherethey are bound by serum albumin and transported to the tissue needing fuel. Once the fatty acids reach the target tissue, they are released by serum albumin and cross into the cytosol. The enzymesused in fatty acid oxidation in animal cells are located in the mitochondrial matrix (as was demonstrated by Eugene P. Kennedy and Albert Lehninger in 1948). Free fatty acid chains of more than 12carbons require the help of membrane transporters to cross into the membrane into the mitochondria, where they undergo Fatty acid degradation.
Fatty acid degradation is the process in which fatty acids arebroken down, resulting in release of energy. It includes three major steps:
• Activation and transport into the mitochondria
• Electron transport chain
Fatty acids are transportedacross the outer mitochondrial membrane by carnitine-palmitoyl transferase I (CPT-I), and then couriered across the inner mitochondrial membrane by carnitine. Once inside the mitochondrial matrix,the fatty acyl-carnitine (such as palmitoylcarnitine) reacts with coenzyme A to release the fatty acid and produce acetyl-CoA. CPT-I is believed to be the rate-limiting step in fatty acid oxidation....