We describe rapid hydrolysis of triglycerides with medium-chain fatty acids in the 1 and 3 positions and a long-chain fatty acid in the 2 position. The triglycerides, 2-linoleoyl-1,3-dioctanoyl glycerol (8L8) and 2-oleoyl-1,3-dioctanoyl glycerol, hydrolyzed more rapidly than triglycerides comprising all long-chain fatty acids. The in vitro hydrolysis rate of 8L8 was similar to that of a medium-chain triglyceride of octanoic and decanoic acids in random positions. From intestinal recovery of 14C 45 min after injection into the isolated, irrigated loop of the small intestine of an anesthetized rat, the amount of 2-[1-14C]linoleoyl-1,3-dioctanoyl glycerol absorbed was greater than 2 1/2 times that of its long-chain analog, 2-[1-14C]linoleoyl-1,3-dioleoyl glycerol. These data support the ease of hydrolysis and absorption of 1,3-dioctanoyl triglycerides with long-chain fatty acids in the 2 position.
Triglycerides are metabolized by most of the organs and tissues of the body. However, the conditions in the lumen of the intestinal tract are unique, for it is only here that triglycerides are metabolized in the free state. Elsewhere these lipids are associated with water-soluble materials. Since the substrate is water-insoluble and the enzyme is water-soluble, lipase, which brings about the hydrolysis of triglycerides in the intestinal tract, has the special property of being capable of functioning efficiently at an oil/water interface. Any material that can alter the nature of this oil/water interface can markedly influence the digestion of triglyeerides.Because of the unusual conditions under which the hydrolysis of triglycerides occurs, the usual methods of studying enzyme kinetics are not applicable. Besides the enzyme-substrate reaction itself, one must consider also such matters as diffusion of the substrate to the oil/water interface, removal of the products of hydrolysis from the oily/water interface, and the subsequent diffusion of these into the bulk phase. All of these steps can be influenced by such variables as efficiency of agitation, electrolyte concentration, and the presence of surface-active agents, such as monoglycerides, soaps, and the bile salts.
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