The activity of these disaccharidases increases after birth and reaches adult levels during the first months of life. Transglucosylation and condensation reactions catalysed by microbial a-glucosidases can convert glucose-containing syrups from starch to a mixture with a high percentage of a-(l→6)-linked oligosaccharides. Dextran polymers of molecular weight 10,000 to 40,000 provide long, hydrophilic arms that can accommodate multiple attachment points for macromolecules along their length. Diagnosis typically requires endoscopy for histologic examination of small bowel morphology and measurement of disaccharidase levels on biopsy specimens. Symptoms may abate with the restriction of carbohydrate in the diet or with the use of enteral sucrase enzyme supplements. Periodate oxidation results in the cleavage of the carbon–carbon bonds between the Nos. The intestinal brush-border enzyme isomaltase cleaves isomaltose into two glucose molecules. Many enzymes associated with the process of digestion and absorption are located on the surface of these microvilli. Reduction of these Schiff base linkages with sodium borohydride or sodium cyanoborohydride results in stable secondary amine bonds, covalently attaching multiple antibody and toxin molecules along the length of the polysaccharide chain (Figure 20.35). Conjugation of antibody molecules to toxins can be performed with dextran to produce immunotoxins suitable for in vivo administration.

Lia Noemi Gerschenson, ... Eliana Noemi Fissore, in Nutraceutical and Functional Food Components, 2017. For this reason, activated dextran may be more useful for constructing antibody conjugates consisting of cytotoxic organic compounds, not protein toxins—for example, chemotherapeutic drugs, hormones, or radioactive complexes. It catalyzes the hydrolysis of trypsinogen into trypsin, a reaction that initiates the activation of pancreatic zymogens in the intestinal lumen. Significant amounts are consumed with many sweet fruits. Exposure to these products leads to osmotic diarrhea, pain, bloating, abdominal distention, and at times, chronic malnutrition and failure to thrive. There is no need to limit starch because of the small percentage of 1-6 linkages in the amylopectin of starch, as pointed out earlier. Martin Kohlmeier, in Nutrient Metabolism, 2003. Periodate oxidation results in the cleavage of the carbon–carbon bonds between the Nos. At least six exo-oligopeptidases have been described that have a wide range of substrate specificity. Fructose, which is not normally present at significant concentrations in blood, is transported by facilitated diffusion. Cancer therapeutic agents such as adriamycin, bleomycin, and daunomycin can be coupled to the oxidized dextran through their amine groups (also see Chapter 1, Section 3.5). All these products have only one way out. Weijers and his colleagues in Holland in 1961 were the first to recognize that diarrhoea in infancy could be caused by a deficiency of the sugar-splitting enzymes, sucrase and isomaltase. These gases form the basis of carbohydrate-specific breath hydrogen testing, which is often used in diagnosis. The disaccharidases have been solubilized from the brush border and partially purified. During early stages following a meal, the concentration of monosaccharides in intestinal fluids may exceed that in the body; thus, sugar transport may be passive and facilitated. After insertion in the brush-border membrane, it is cleaved into sucrase and isomaltase units that reassociate noncovalently. Palatinose™ or Isomaltulose, is a naturally sourced carbohydrate which smoothens the impact on blood sugar levels. Voglibose was marketed (Basen®) as an antidiabetic agent in 1984 in Japan. Amylose, the α-(1>4) Glc polymer with a molecular weight of around 60 kD, typically comprises about 20% of starch in plants and is thus consumed with many foods. Dextran is a structurally heterogeneous glucan containing linear and branched sequences with a preponderance of 1,6-α-d (isomaltose) and a smaller percentage of 1,2-α, 1,3-α, and 1,4-α-d linkages. Glc is combined with other monosaccharides in sucrose and lactose. The terminating monosaccharide in a dextran polymer is often a fructose group. Patients who develop gas, bloating, or diarrhea after the ingestion of mushrooms may have a deficiency in the disaccharidase trehalase. About two-thirds of carbohydrate intake in developed countries is Glc. Whenever lactose goes undigested, it is not absorbed and passes into the large intestine. Chemoimmunoconjugates or antibody–drug conjugates (ADCs) consisting of anticancer agents attached to antibody targeting molecules also can be formed using oxidized dextran carriers.
Lactase activity is highest at birth and decreases gradually during the neonatal period. Certainly, only intact A–B toxins have a chance of succeeding with this method, since A chain or single-subunit toxins would not be capable of release from the complex after cellular docking. Transformation of maltose into isomalto-oligosaccharide can also be achieved using α-glucosidase enzymes (E.C. Starch is degraded first to dextrins and then to a mixture of glucose, maltose, and isomaltose (containing the α-1,6 linkages that are not digested by amylase). The mucosa also contains two enzymes with lactase activity. Table 14-6. Amylose provides 8–10% of the energy in a mixed diet in the United States. About two-thirds of carbohydrate intake in developed countries is Glc.

Sucrase and isomaltase have been purified together as a two-enzyme complex (Gray et al., 1979; Kolinska and Semenza, 1967), and this enzyme complex accounts for the total hydrolysis of the products of amylase digestion (Gray et al., 1979; Rodriguez et al., 1984).
The brush border epithelium of the small bowel contains enzymes necessary for carbohydrate digestion. The other lactase hydrolyzes lactose readily. At later stages and for most of the digestive process, transport of monosaccharides from the gut into the bloodstream occurs against a concentration gradient; carbohydrate absorption is primarily an active process. During early stages following a meal, the concentration of monosaccharides in intestinal fluids may exceed that in the body; thus sugar transport may be passive and facilitated. The difference between the two disaccharides is that an α-(1→4) bond connects the two glucose parts in maltose while in isomaltose they are linked by an α-(1→6) bond. In addition to starch, the other major dietary carbohydrates are the disaccharides lactose and sucrose, and the monosaccharide fructose. Whenever lactose goes undigested, it is not absorbed and passes into the large intestine. The onset of various carbohydrate malabsorption syndromes can vary based on the timing of the introduction of particular carbohydrates (Table 11.12). Carbohydrate malabsorption is secondary to either deficiency of a particular enzyme (e.g., congenital sucrase-isomaltase deficiency) or an abnormality in a transport protein involved with the absorption of monosaccharides (e.g., glucose-galactose malabsorption).

Palatinose™ can be used in many food applications.

The monosaccharides produced by complete digestion of these dietary carbohydrates are glucose, galactose, and fructose. On paper this is just a different number but for the enzyme that has to split the disaccharide it is an entirely different job. Maltose and isomaltose are the disaccharides (glucose-glucose) produced as end products of starch digestion. All these products have only one way out. They rpoduce each about 4,000 tons per year(3). Glucose and galactose are transported by an Na+/K+-ATPase from lumen into epithelial cell. Recent data obtained with FOS demonstrate that the dose and the duration of oligosaccharide intake, the location of fermentation (proximal or distal colon), as well as the initial composition of fecal flora, are important factors influencing the extent of the prebiotic effect, that is, the increase in Bifidobacteria (Rao, 2001; Tuohy et al., 2001a,b). These mutations result in a variety of defects in the structure and function of the enzyme, including isolated deficiencies in sucrase activity or isomaltase activity. Even intact two-subunit toxins, however, may not be capable of releasing an A chain unit, due to the multivalent nature of the oxidized dextran linker. Wird dieses Enzym von der Darmschleimhaut nicht in ausreichender Menge produziert, kommt es zu einer Isomaltoseintoleranz. Acarbose was marketed in Germany in 1990 for the treatment of diabetes under the name Glucobay®. The condition may present with intermittent watery diarrhoea, and sometimes with incontinence with intermittent abdominal distension and crampy abdominal pain in the older child. The active site for isomaltase is close to the membrane, whereas the active site for sucrase is located distally. There are three of these enzymes, all of which have dual function and two different active sites within the same molecule. The monosaccharides produced by complete digestion of these dietary carbohydrates are glucose, galactose, and fructose. Enzymes of the Intestinal Brush Border. The human sucrase-isomaltase is a dual-function enzyme with two GH31 domains, one serving as the isomaltase, the other as a sucrose alpha-glucosidase. Lactase–phloridzin hydrolase is another dual enzyme, with its C-terminal end facing the cell interior. They found that all parents had deficient intestinal sucrase and isomaltase levels. IMO is formed by enzyme-catalyzed hydrolysis of starch from different cereal crops (wheat, barley, corn), pulses (lentils, peas), rice, tapioca (cassava), potato, and other starch sources. Starch is degraded first to dextrins and then to a mixture of glucose, maltose, and isomaltose (containing the α-1,6 linkages that are not digested by amylase). Miglitol was introduced onto the market in 1999 with the name Diastabol® for treatment of diabetes type 2.13,13a Salacinol 13 and kotalanol 14 were isolated from the water-soluble fraction of the roots and stems of Salicia reticulata14,14a and used for treatment of diabetes in traditional Indian medicine; these compounds have been found to be potent inhibitors of α-glucosidase (IC50 1.1 nM and 0.38 μM, respectively). Fructose, which is not normally present at significant concentrations in blood, is transported by facilitated diffusion.

The terminating monosaccharide in a dextran polymer is often a fructose group. We use cookies to help provide and enhance our service and tailor content and ads. Acid hydrolysis of polysaccharides tends to yield unacceptably high levels of the monosaccharide (Turvey and Whelan, 1957), so enzymatic approaches are generally preferred. It was proposed that all these enzyme activities represent one protein under a single gene control (Dawson, 1970). The main repeating unit is an, ). The disaccharidases have been solubilized from the brush border and partially purified. Bioavailable food sources are monomeric Glc, oligosaccharides and polysaccharides containing only Glc (starches, maltodextrin, maltose, isomaltose, and trehalose in plant foods, and glycogen in animal foods), and the mixed disaccharides lactose (α-d-galactopyranosyl-[1>4) d-glucose] and sucrose [Glc α-(1>β2] fructose). Partial chemical or enzymatic hydrolysis of dextran results in low-molecular weight dextrans and oligosaccharides. GA, glucoamylase. Patients with carbohydrate malabsorption disorders present with severe watery diarrhea, which results from osmotic action exerted by the malabsorbed carbohydrate in the intestinal lumen. IMO is found to be effective at increasing the number of Bifidobacteria and lactate and at improving the intestinal microflora in general and is therefore safe to categorize as a prebiotic (FDA, 2005a). It is absorbed from the intestine and metabolized slowly by isomaltase, but the rate of insulin stimulation is very low. Secondary lactase deficiency with clinical signs of lactose intolerance can be seen in celiac disease, Crohn disease, and immune-related and other enteropathies and should be considered if children with these diagnoses have symptoms of lactose intolerance. The mechanism of diarrhea in these disorders is osmotic.

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