Enzymes lipoprotein lipase

Intravenous lipid emulsion particles are hydrolyzed in the bloodstream by the enzyme lipoprotein lipase to release free fatty acids and glycerol. Free fatty acids then are be taken up into adipose tissue for storage (triglycerides), oxidized to energy in various tissues (e.g., skeletal muscle), or recycled in the liver to make lipoproteins. 

A schematic representation of the metabolism of lipoproteins is shown in Fig. 12 [170]. Chylomicrons are synthesized and secreted by the small intestine. They are hydrolyzed in blood by the enzyme lipoprotein lipase... 

Figure 7.4 Fate of triacylglycerol that is present in fuel blood after secretion by the intestine. The dietary triacylglycerol in the intestine is hydrolysed to long-chain fatty acids and monoacyl-glycerol, both of which are taken up by the enterocytes in which they are then re-esterified. The triacylglycerol is released in the form of chylomicrons into the blood, from where it is hydrolysed to fatty acids and glycerol by the enzyme lipoprotein lipase in specific tissues (Figure 7.3). The fatty acids are taken up by adipocytes, muscle fibres and secretory cells in the mammary gland.

In the capillaries of these tissues, the extracellular enzyme lipoprotein lipase, activated by apoC-II, hydrolyzes triacylglycerols to fatty acids and glycerol (step... 

These lipids are then packaged into spherical lipoproteins, particles of lipids and proteins, known as chylomicrons, which are secreted into lymphatic vessels and subsequently enter the blood stream. Once in the circulatory system the triacylglycerol components of the chylomicrons are degraded to fatty acids and glycerol by the enzyme lipoprotein lipase, which is attached to the luminal (inner) side of capillary vessels in heart, muscle, adipose (commonly... 

The action of an enzyme lipoprotein lipase in adipose tissue depletes chylomicrons and VLDLs of their triacylglycerol. The enzyme is activated by apolipoprotein C, with which it specifically interacts on the surface of chylomicrons and VLDLs. 

Apoliproteins the surface proteins of lipoproteins apoli-proteins AI and All are the major apoliproteins of HDL apo CII is a lipoprotein present on chylomicrons and VLDL which activates the enzyme lipoprotein lipase. 

The liver is responsible for synthesis of cholesterol, high-density lipoproteins, and very-low-density lipoproteins. The enzymes lipoprotein lipase and lecithin-cholesterol acyltransferase also are synthesized in this organ. Increased serum triglyceride and FFA concentrations are encountered in patients with hepatic failure, primarily due to the increased lipolysis. The significant insulin resistance that can be seen in cirrhosis causes a shift to lipids as a fuel source. Whereas only 35% of total calories are derived from fat in normal patients after an overnight fast, this can increase to 75% in patients with cirrhosis. Incorporation of late evening snacks in patients with liver cirrhosis may correct abnormal substrate metabolism, increase carbohydrate, and decrease fat oxidation rates. ... 

In the capillaries of these tissues, the extracellular enzyme lipoprotein lipase, activated by apoC-II, hydrolyzes triacylglycerols to fatty acids and glycerol (step ), which are taken up by cells in the target tissues (step (7)) In muscle, the fatty acids are oxidized for energy in adipose tissue, they are reesterified for storage as triacylglycerols (step (8)). 

Which one of the following apoproteins acts as a cofactor activator of the enzyme lipoprotein lipase (LPL) ... 

With this state of uncertainty, it is not possible to define the true structural and functional role of the chylomicron protein. Chylomicrons are generally considered as a large central sphere of glycerides with small amounts of cholesterol, phospholipid, and protein loosely adsorbed on the surface, forming, according to Lindgren and Nichols (1960), small lipoprotein subunits. Aside from physical stabilization, the adsorbed components at the surface appear to impart biochemical specificity to the chylomicron particles, as indicated by Korn s studies (1955) showing that chylomicrons, and not simple fat emulsions, form an optimal substrate for the enzyme lipoprotein lipase. 

Chylomicrons, These contain mostly triglyceride with only a small proportion of protein. They are formed from triglycerides absorbed from the diet. They are transported to the tissues (especially adipose tissue) where they are broken down by the enzyme lipoprotein lipase. 

They can be synthesized by the gut, following the absorption of hydrolyzed dietary lipid. They are combined with small amounts of protein, cholesterol and phospholipid to form chylomicrons. These are removed from the blood, mainly by adipose tissue. An enzyme, lipoprotein lipase is responsible for this hydrolysis of the chylomicron triglycerides. The free fatty acids liberated by these processes are resynthesized into triglycerides by the adipose tissue and stored. 

In animals, net triacylglycerol synthesis occurs when energy demands exceed immediate requirements. Most diets contain both fat and carbohydrates, but when there is a preponderance of energy as carbohydrates, the tissues convert them into fatty acids which are then esterified into acylglycerols. When there is a preponderance of fat in the diet, fat synthesis from carbohydrate is depressed in the tissues. The products of fat digestion are then converted into lipoproteins (section 5.3) which circulate in the bloodstream. When the lipoproteins reach the tissues, fatty acids are released from the acylglycerols at the endothelial surfaces of cells, a process catalysed by the enzyme lipoprotein lipase, and are taken up into the cells... 

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