Monoacylglycerols

These partially acylated glycerols are usually present only in trace amounts in fresh tissues. They can be analyzed analogously to TAGs using any of the techniques mentioned above [79]. 

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The mixed micelles contain predominantly FFAs, 2-monoacylglycerols, and unesterified cholesterol in addition to other fat-soluble compounds, such as the fat-soluble vitamins A, D, E, and K. 

Correct answer = A. Pancreatic lipase hydrolyzes dietary triacylglycerol primarily to 2-monoacylglycerol plus two fatty acids. These products of hydrolysis can be absorbed by the intestinal mucosal cells. Bile salts do not inhibit release of fatty acids from triacylglycerol, but rather are necessary for the proper solubilization and hydrolysis of dietary triacylglycerol in the small intestine. Short- and medium-chain length fatty acids enter the portal circulation after absorption from the small intestine. Synthesis of apolipoproteins, especially apo B-48, is essential for the assembly and secretion of chylomicrons. 

Correct answer = E. Chylomicrons contain a lipid core that is composed of dietary lipid and lipid synthesized in the intestinal mucosal cells. Free fatty acids are esterified primarily to 2-monoacylglycerol. forming triacylglycerol, prior to export from the intestinal mucosal cells in chylomicrons. Mixed micelles are found only in the lumen of the small intestine. 

The products of lipid digestion—free fatty acids, 2-monoacylglycerol, and cholesterol—plus bile salts, form mixed micelles that are able to cross the unstirred water layer on the surface of the brush border membrane. Individual lipids enter the intestinal mucosal cell cytosol. 

Typical thin-layer chromatogram of lipids. The solvent system, hexane-diethyl ether-acetic acid (90 10 1). (1) cholesterol, (2) fatty acid, (3) triacylglycerol, (4) fatty acid methyl ester, (5) cholesterol ester, (6) glycerophosphatide, (7) sphingolipid, (8) 1,3- or 1,2-diacylglycerol, (9) 1 - or 2-monoacylglycerol. The Rf for (5), cholesterol ester, is calculated as follows ... 

Innis, S.M., Dyer, R., Nelson, C.M. 1994. Evidence that palmitic acid is absorbed as sn-2 monoacylglycerol from human milk by breast-fed infants. Lipids 29, 541-545. 

Question By what mechanism do the fatty acids and 2-monoacylglycerol enter the circulation ... 

Lipoprotein lipase is an extracellular enzyme that hydrolyzes triacylglycerol into 2-monoacylglycerol and two fatty acids. The fatty acids then enter the cell passively down a concentration gradient. 

In the intestine, triacylglycerol synthesis also occurs in the ER membrane, but fatty adds are esterified with 2-monoacylglycerol, as follows ... 

Diacylglycerols (DAGs) content of commercial oUs varies from 2% to 11% (2). Monoacylglycerols (MAGs) content of WGO (0.1-1.0%) is usually lower than the DAG content. It had been also reported that fatty acid composition of MAG was significantly different than that of the other acyl lipids (32). Linoleic acid content of MAG was significantly lower than that of the other acyl lipids. 

A small intestine, where the fat is emulsified by bile salts the triacylglycerols are hydrolyzed at the sn-1 and sn-3 positions by pancreatic lipases at nearneutral pH to produce fatty acids and n-2-monoacylglycerols and these products are absorbed by several alternative processes. 

The digestion of triacylglycerols in adult nonruminant mammals has been described as initiated in the mouth by hngual lipase released in the sahva at the base of the tongue (52). Up to 6% of the fatty acids are hydrolyzed and initiate emulsion formation in the stomach. The digesta (called chyme at this location) is released from the stomach slowly into the duodenum to ensure complete mixing with the bile salts and emulsification. Lipolysis occurs by association of pancreatic lipase and co-lipase at the surface of the bile salt-stabihzed emulsion. Amphipathic molecules (fatty acids, sn-2 monoacylglycerols, and lysolecithins) are produced and associate with the bile salts to form water-soluble micelles from which absorption occurs. 

Fats Come From Two Main Sources stored body fat and dietary fat. Dietary fat must first be emulsified to increase its surface area for contact with the water soluble lipases. This occurs largely in the duodenum after mixing with the bile acids, a family of cholesterol derived detergents. Triacylglycerols can then be hydrolyzed by pancreatic lipase to free fatty acids and 2-monoacylglycerol ... 

The dietary triacylglycerols, which are water-insoluble, are digested in the small intestine to fatty acids and 2-monoacylglycerols. These digestive products are resynthesized to triacylglycerols in intestinal epithelial cells and are secreted in chylomicrons via the lymph into the blood. 

Pancreatic lipase, with the aid of colipase, digests the triacylglycerols to 2-monoacylglycerols and free fatty acids, which are packaged into micelles. The micelles, which are tiny microdroplets emulsified by bile salts, also contain other dietary lipids such as cholesterol and the fat-soluble vitamins. 

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