Figure 4 Chylomicron pathway. The reactions in this initial stage are the same as in ketogenesis (see slide 10.4.1).However, while ketogenesis occurs in the mitochondria, HMG-CoA destined for … The pharmaceutical industry has taken advantage of this knowledge to lower people's LDL levels with drugs known as statins. Abnormalities in chylomicron (apolipoprotein B-48-containing lipoproteins) metabolism are associated with risk of pancreatitis. The Pathways of Lipid Transport. (2) Chylomicron Metabolism Chylomicrons are metabolized in adipose tissue and muscle. Chylomicrons enter the circulation and travel to peripheral sites. Plasma concentrations of chylomicrons and chylomicron remnants give no insight into the magnitude of substrate flux through these pathways. The triglycerides carried in VLDL are metabolized in muscle and adipose tissue by lipoprotein lipase releasing free fatty acids and IDL are formed. Triglycerides are formed in the intestinal cell from free fatty acids and glycerol and cholesterol is esterified. Exogenous pathway for lipid metabolism: Dietary cholesterol and fatty acids are absorbed. These surface constituents are transferred from the chylomicron remnant for the formation of high density lipoprotein. Triglycerides and cholesterol combine to form chylomicrons. Chylomicron remnants are then taken up by the liver. Rate-limiting enzymes limit the rate at which a metabolic pathway proceeds. Empty HDL is produced as a byproduct of steps 3 and 4. The endogenous pathway of lipid metabolism begins with Exogenous cholesterol metabolism pathway Endogenous Pathway. 6. for which apo E is a high-affinity ligand. The enterocyte re-esterifies fatty acids and monoglycerides to form triglycerides and phospholipids. The endogenous lipoprotein pathway begins in the liver with the formation of VLDL. Chylomicrons are the ‘orphans’ of the lipoprotein family. Chylomicron Metabolism Since the intestine is primarily an absorptive organ, it must have the means of exporting newly absorbed lipids. 1. After unloading their fats, chylomicrons are smaller and referred to as chylomicron remnants. These drugs inhibit HMG-\(\ce{CoA}\) … The chylomicron remnants contain a smaller core of lipids that is enveloped by excess surface components. There are three main pathways responsible for the generation and transport of lipids within the body. The intestine secretes chylomicron particles into the lymphatics. Difficulty of measurement has impeded understanding of their metabolism. Very-low-density lipoproteins (VLDL) contain apoprotein B-100 (apo B), are synthesized in the liver, and transport TGs and cholesterol to peripheral tissues. 5. Chylomicron remnants then travel to the liver and are removed by the binding of apoE to their remnant receptor. 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