Abstract
Little is known regarding intestinal lipase, although its participation in the absorption of neutral fat from the gastrointestinal tract has been suggested (1). Lipolysis by intestinal enzymes was first established by Schiff (2) in studies with depancreatized dogs. Kalaboukoff and Terroine (3) later reported that glycerol extracts of intestinal mucosa hydrolyzed olive oil and that this activity was accelerated by the addition of bile salts. In this study, the lipase activity of intestinal mucosa has been examined. In order to limit the study to lipase activity, we have employed long chain triglycerides as substrate in the form of olive oil emulsions. As will be seen, the intestine also contains aliesterases, as judged by the rapid hydrolysis of short chain fatty acid esters. These enzymes would not be expected to interfere with lipase estimations, since, in other tissues such as the liver, they have been shown to be completely inactive toward long chain triglycerides. The pancreatic enzyme has generally been regarded as the prototype of lipases. We have therefore compared the intestinal and pancreatic enzymes with regard to substrate specificity and the effects of various activators and inhibitors, a number of which have been employed by other investigators to characterize esterolytic enzymes. Although the intestinal activity appears to be similar, in general, to that of the pancreas, it is clear that the enzymes involved are not identical. The possible participation of intestinal lipase in the intestinal absorption of fat is discussed.
Highlights
Intestinal lipase activity was reduced by 50% in the presence of 1 X 1O-3 M quinine
Substrate Speci$city-When intestinal lipase activity was tested by incubating the preparation with equivalent concentrations of l-mono, 1,3 di, triolein it was found that the rates of hydrolysis of all three glycerides were identical within the limits of experimental error (Fig. 7)
The lipase activity of hog intestinal homogenate as measured by the hydrolysis of olive oil emulsion was divided between the soluble fraction and the particulate fraction consisting of mitochondria and microsomes
Summary
Preparation of substrate-For routine assay of lipase activity, olive oil was employed as substrate. The supernatant containing the mitochondria and microsomes, after removal of the white lipid scum, was stored at -20” This fraction is referred to as the duodenal homogenate; its protein content was determined to be approximately 15 mg per ml by the method of Gornall et al [8]) modified to give a final NaOH concentration of 0.8 N. The enzyme preparation employed was a cell-free homogenate of hog duodenum and contained 14.6 mg of protein per ml. Hollett and Meng [12] failed to show fluoride inhibition of the pancreatic enzyme at the concentration employed in this study, this has been reported by others [13] This discrepancy may be explained by the observation that fluoride will partially inhibit the stimulatory effect of protein on pancreatic lipase. 2.5 x 1O-3 M fluoride when the pancreatic enzyme was tested in the presence of 1% serum albumin or as a crude homogenate
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