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Specificity of the Human Intestinal Disaccharidases and Implications for Hereditary Disaccharide Intolerance

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SPECIFICITY OF THE HUMAN INTESTINAL DISACCHARIDASES AND IMPLICATIONS FOR HEREDITARY DISACCHARIDE INTOLERANCE Arne Dahlqvist J Clin Invest. 1962;41(3):463-470. https://doi.org/10.1172/JCI104499. Research Article Find the latest version: https://jci.me/104499/pdf Journal of Clinical Investigation Vol. 41, No. 3, 1962 SPECIFICITY OF THE HUMAN INTESTINAL DISACCHARIDASES AND IMPLICATIONS FOR HEREDITARY DISACCHARIDE INTOLERANCE * By ARNE DAHLQVIST (From the Department of Physiological Chemistry, University of Lund, Sweden) (Submitted for publication June 27, 1961; accepted October 27, 1961) The existence of several different a-glucosidases 1) Jejunal sample, from a 40 year old woman; resection has recently been demonstrated in extracts of pig of the middle part of the small intestine was indicated by an intestinal tumor. From an 8-cm piece of normal intestinal mucosa (1-7). These enzymes have intestine, located in the distal decimeters of the jejunum, varying specificity for disaccharides with a-D-glu- 1.6 g of mucosa was scraped off with a glass slide. The copyranoside structure (e.g., maltose, sucrose, iso- mucosa was homogenized for 1 minute in an Ultra-Tur- maltose, trehalose), and thus the intestinal hy- rax homogenizer with 4.8 ml of 0.9 per cent NaCl, the drolysis of these sugars is caused by a more com- tube being chilled with crushed ice during homogenization. previously After removal of nuclei and greater cell debris by cen- plicated enzyme mixture than had been trifugation in an ordinary laboratory centrifuge (Wifug, believed (8, 9). rotor no. 103-30A, 4,000 rpm) for 10 minutes, the opales- The 8-glucosidase and /3-galactosidase activities cent supernate, which contains the disaccharidases (22), of extracts of pig intestinal mucosa, in contrast, was used for analysis. 2) Ileal sample, from a 26 year seem to be exerted by one enzyme, intestinal lac- old woman suffering from chronic ulcerative colitis; re- operation of ileocecal anastomosis indicated by abdominal tase (10, 11). abscess. A 15-cm piece of the distal part of the ileum It is not known whether the specificity of the was removed. The intestinal wall of this piece showed human intestinal disaccharidases parallels that of considerable induration, but the mucosa appeared macro- the pig enzymes. This question is of clinical im- scopically normal; 3.0 g of mucosa was obtained by portance, however, since several cases of hereditary scraping with a glass slide. The mucosa was homoge- nized as described above with 9.0 ml of 0.9 per cent inability to digest certain disaccharides have been NaCl. recently described, and are apparently caused by Assay of disaccharidase activities was performed by inherited deficiency of single intestinal disacchari- the methods previously described (23, 24) using the dases (12-19). Tris-glucose oxidase reagent (24). One unit of disac- Since the human intestinal content, obtained by charidase activity causes 5 per cent hydrolysis in 2.0 ml a catheter during the digestion of a meal, contains of 0.028 M substrate, which is equal to the formation of 1 mg monosaccharide (23), in 60 minutes at 370 C and at essentially no disaccharidases (20, 21), this ma- optimum pH. terial cannot be used for the study of the specificity Assay of polysaecharidase activities was done as previ- of these enzymes. Therefore homogenates have ously described (25). One unit of amylase or dextranase been prepared of human intestinal mucosa, ob- activity catalyzes an increase in reducing power corre- tained from pieces of small intestine cut out during sponding to 1 mg of disaccharide (monohydrate) in 60 minutes at 370 C, and may thus be compared with the surgical operations. These homogenates had unit for disaccharidase activity. powerful disaccharidase activities, and the speci- Assay of protein was performed by the method of ficity of the enzymes responsible for these activi- Lowry, Rosebrough, Farr and Randall (26) with the ties has been studied by heat inactivation. modified reagent B introduced by Eggstein and Kreutz (27). A standard curve was prepared with human serum by AB Kabi (Stockholm). AND METHODS albumin, kindly supplied MATERIALS Heat inactivation. When a solution of an enzyme is Homogenates of human intestinal mucosa. Two sam- heated at a sufficiently high temperature the enzyme is ples were obtained, one from the distal part of the inactivated, following the kinetics of a first-order reac- jejunum, and the other from the distal part of the ileum. tion. The temperature interval within which the velocity constant for the inactivation increases from zero (no * This investigation was supported by grants from the measurable inactivation) to very high values (complete Swedish Medical Research Council and the Royal Physi- inactivation within a few minutes) is usually less than 100. ographic Society at Lund, Sweden. Since the different glycosidases present in extracts of pig 463 464 ARNE DAHLQVIST intestinal mucosa have widely different sensitivities to paper indicate that the human intestine contains disac- heat, fractionated heat inactivation provided a useful charidases which are essentially similar to the correspond- method for the separation of these enzymes (3, 28, 29). ing enzymes of the pig, although some differences are The rate of the heat inactivation at a certain tempera- found. The chromatographic separation of the pig en- ture is strongly dependent on the pH of the solution; zymes succeeded only with the use of a special tech- thus an appropriate buffer must be added. It is also nique-mutual displacement chromatography (29)- desirable to heat the enzyme solution to the desired in- which demanded rather large amounts of enzyme ma- activation temperature as quickly as possible and then to terial. The limited amount of enzyme available with hu- maintain this temperature within 0.10 during the ex- man preparations prohibited separation experiments with periment. The enzyme solution which is to be inacti- this method. Chromatographic separation of the human vated (usually a volume of 5 to 10 ml) was therefore disaccharidases will have to await the development of a first immersed in a preheating bath that had a tempera- suitable micromethod. ture 7° to 80 higher than the inactivation bath. Dur- RESULTS ing the preheating the tube was continously shaken, and the temperature of the enzyme solution was measured The homogenates had powerful disaccharidase with a thermometer having 0.10 gradations. At the activities. The relative rate of hydrolysis of dif- moment the desired inactivation temperature was reached (under these conditions this occurred in less than 1 min- ferent disaccharides was essentially the same as ute) the tube was transferred to the inactivation bath; at that reported earlier for preparations from the mu- the the same time a zero-time sample was taken for en- cosa of the adult pig (23, 25), except that the rela- zyme analysis and a stopwatch was started. Care was tive isomaltase activity of the human preparations taken that the inactivation temperature was never ex- was stronger and the trehalase activity somewhat ceeded during preheating. New samples for enzyme analy- sis (0.5 to 1 ml) were withdrawn at intervals, immedi- weaker than in the pig (Table I). ately blown down into tubes chilled with crushed ice, and The lactase activity of the jejunal sample was so stored until analyzed. strong, but this activity was practically absent in The enzyme solutions for heat inactivation in the pres- the ileal sample, indicating that lactase in the hu- ent case were prepared by mixing 1 vol of homogenate man is localized in the proximal part of the in- (the j ejunal sample, which was strongest in disaccharidase activity, had first been diluted 1:2 with distilled water) testine as it is in the pig (25). This is also in ac- with 4 vol of 0.0125 M sodium phosphate buffer, pH 7.0. cordance with the finding that lactose is absorbed Validity of separation by heat inactivation. The sepa- in the proximal part of he human small intestine ration of two enzymatic activities, present in the same (21). preparation, only on the basis of their different sensitivi- The cellobiase and gentiobiase activities in the ties to heat, does not conclusively prove that the two ac- (Table tivities are manifestations of different enzyme proteins; two samples paralleled the lactase activity heating the solution may affect activators or inhibitors, I), indicating that also in the human intestine breaking single bonds within the enzyme molecule may ,8-glucosides and /3-galactosides may be hydrolyzed alter the specificity of the enzyme, and so forth. In- by a single enzyme (10, 11). versely, the parallel heat inactivation of two different en- zymatic activities does not necessarily mean that these are caused by the same enzyme; two different enzymes TABLE I may very well have similar heat inactivation properties. Carbohydrase activities of the homogenates of human small The results of heat inactivation experiments therefore intestinal mucosa * must be compared with those of other separation meth- ods, such as fractionation with different precipitants, Carbohydrase a) Jejunal b) Ileal electrophoresis, ion-exchange chromatography, and so on. activity sample sample the existence of several different disac- By such methods unitsIg mucosa charidases in pig intestinal mucosa has been conclusively Maltase (total) 948 292 demonstrated and the specificity of the different enzymes I nvertase 360 40 elucidated (3-7, 10, 28-30). In this study the results of Isomaltase 272 69 Trehalase 31 17 the heat inactivation experiments agreed very well with Turanase 74 23 those of the other methods. Furtthermore, the heat in- Palatinase 59 12 activation analysis was found to be the most simple and Lactase 412 3.2 accurate method for the analysis of the mixture of disac- Cellobiase 78 0.6 Gentiobiase 2.4 0.0 charidases present in extracts of pig intestinal mucosa Amylase 1,328 960 (3, 29).
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