Intestinal Invertase

D-Fructose in the human diet derives mainly from sucrose, fruits, and honey. Sucrose is /I-D-fructofuranosyl a-D-glucopyranoside, and, after hydrolysis by invertase (EC 3.2.1.26), to D-glucose and D-fructose, can be absorbed from the small intestine. In the human intestine, invertase, as well as a-D-glucosidases, is developed very early in fetal life, and even appears much earlier than lactase (EC 3.2.1.23). There is no significant, intestinal transport of unhydrolyzed sucrose, and, in animal experiments, sucrose administered by injection is quantitatively excreted in the urine.1 Intestinal invertase is produced by mucosal cells localized in the brush-border membrane of the mucosal epithelia. Invertase is not secreted,1-4 and little or no invertase (sucrase) has been found in the intestinal lumen.1 The specific localization of sucrase at the mucosal, luminal interface is thought to be of functional importance in coupling sucrose digestion to transport.1... 

Invertase (sucrasc) small intestine, yeast sucrose glucose and fructose 6 2 (gut) 4 8 (yeast)... 

In 1896, Fischer developed the phenylhydrazine test" for the detection of hydrolytic scission of disaccharides, especially by enzymes this depends on the fact that the phenylosazones of disaccharides are soluble in hot water, whereas those of the monosaccharides are not. Lactose is hydrolyzed by emulsin (1894) and by lactase it is not fermentable by yeast, and is unaffected by invertase (1894). An extract of the small intestine of horses and cattle, especially from young animals, hydrolyzes lactose (1896). The action of enzymes on lactose allowed it to be classified, along with cellobiose and maltose, with the normal (and not the y-type of) methyl glucoside (1914). In the discussion of maltose, the relationship of lactose to the /9-series will be mentioned later. 

In the mammal, complex polysaccharides which are susceptible to such treatment, are hydrolyzed by successive exposure to the amylase of the saliva, the acid of the stomach, and the disaccharidases (e.g., maltase, invertase, amylase, etc.) by exposure to juices of the small intestine. The last mechanism is very important. Absorption of the resulting monosaccharides occurs primarily in the upper part of the small intestine, from which the sugars are earned to the liver by the portal system. The absorption across die intestinal mucosa occurs by a combination of active transport and diffusion. For glucose, the aclive transport mechanism appears to involve phosphorylation The details are not yet fully understood. Agents which inhibit respiration (e.g., azide, fluoracetic acid, etc.) and phosphorylation (e.g., phlorizin), and those which uncouple oxidation from phosphorylation (e.g., dinitrophenol) interfere with the absorption of glucose. See also Phosphorylation (Oxidative). Once the various monosaccharides pass dirough the mucosa, interconversion of the other... 

As shown by electron microscopy, selective digestion by papain releases the small protruding knobs from the membrane surface of the brush border of intestinal epithelial cells while leaving the unit membrane intact. After separation of the knobs and membranes by differential centrifugation, all the invertase and maltase activities of the brush border were found in the knobs 171). 

A fructan. See Fructans, F-43. Produced by the action of yeast invertase on a cone, sucrose soln. Constit. of the grasses Lolium multiflorum and Arrhe-natherum elatius. Widely distributed in cereals and other grasses. Also isol. from onion (Allium cepa). Component of Neosugar which is a mixt. with Nystose, N-87 and its 1-fructosyl deriv. used as a dietary constit. for improvement of intestinal flora. 

The intestinal mucosa secretes an alkaline, watery juice containing several enzymes. This secretion mixes with pancreatic juice and bile to form the intestinal juice. The succus entericus, a pure intestinal secretion, is a thin liquid consisting of water, bicarbonate, and a few enzymes. Among the enzymes found in the intestinal secretion are exopeptidase, aminopeptidase, amylase, maltase, invertase, lactase, lipase, and entero-kinase, which activates trypsinogen. 

Food contains one polysaccharide (starch) and three disaccharides (maltose, sucrose, and lactose). Salivary and pancreatic amylase digests starch to yield maltose and sucrose, and lactose to yield maltose and sucrose. Sucrose, maltose, and lactose are split by invertase, maltase, and lactase, respectively. The products of the disaccharidase reactions are fructose, glucose, and galactose. Whenever amylase or one of the disacchari-dases is absent from the intestinal content, the undigested sugars pass in the lower part of the intestinal tract and are fermented by the bacterial flora. As a result, lactic acid and volatile acids are formed and stimulate peristalsis and fluid secretion by the intestinal mucosa. Liquid foaming acid and foul-smelling feces are emitted. Amylase may be absent in pancreatic disease. Inborn errors characterized by the absence of intestinal lactase, maltase, and invertase have been described. 

Sucrase (also called saccharase and invertase) hydrolyzes sucrose. In contrast to the abundant information available on the yeast invertase, little is known of the mammalian sucrases. The significance of invertase and lactase in absorption is illustrated by inborn errors of metabolism in which these two enzymes are absent in the intestinal secretion. (The fact that lactase deficiency does not interfere with growth indicates that the galactose needed for biosynthesis of brain lipids or lens proteins can be synthesized endogenously in amounts sufficient to fulfill the metabolic requirements.) In that case, there is an intolerance to lactose or sucrose with no increase in blood glucose levels or without an increase in the levels of disaccharides... 

Brown HT, Heron J. Some observations upon hydrolytic ferments of the pancreas and small intestine. Proc R Soc Lond 30 393-407, 1880. Invertase of the small intestine was also identified by Paschutin V. Einige Versuche mit Fermenten, welche Starke und Rohr-zucker in Traubenzucker verwandeln. Arch Anat Physiol Wissensch Med 305-384, 1871 and by Bierry H. Saccharose spaltende Fermente. Biochem Z 44 415-425, 1912. 

Invertase has been found widely distributed in microorganisms, plants, and animals, The best-studied enzymes are those of yeast and other fungi. In higher animals invertase is produced only in the intestinal mucosa and acts only as a digestive enzyme. 

Crane (1966) has theorized that the brush border plasma membrane is the site of a mosaic of the enzymes associated with the microvillus. This was based on experiments of Eichholz and Crane (1965) who recovered a fraction of pure microvillous membranes by density gradient centrifugation of brush border homogenate which possessed the total activities of alkaline phosphatase, maltas and sucrase and various peptidases. Evidence in favor of this idea was also collected by Johnson (1967) who demonstrated the presence of knobs 60 A in diameter on the glycocalyx of the luminal side of the plasma membrane which contained the brush border invertase and maltase (see Fig. 6). These knobs could be removed entirely from the microvilli of hamster intestine by papain digestion the remaining membrane, however, still has the alkaline phosphatase incorporated into it (Eichholz, 1969 Oda and Seki, 1966). 

Other carbohydrates found in foods, such as sucrose and lactose, are hydrolyzed by specific enzymes, -fructosidase (invertase) and -galactosidase (lactase) that are located in the brush border cells of the human small intestine. There are specific permeases in the small intestine wall for transporting D-galac-tose and D-fructose into the blood. 

Sucrase, or saccharase (invertase). yeast, intestinal secretions sucrose fructose -p glucose. 

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