Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.108 (lactase)
 2,133 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We studied the general mechanism for regulation of glucoamylase and pullulanase synthesis in Clostridium thermohydrosulfuricum. These amylases were expressed only when the organism was grown on maltose or other carbohydrates containing maltose units. Amylase synthesis was more severely repressed by glucose than by xylose. Catabolite repression-resistant mutants were isolated by using nitrosoguanidine treatment, enrichment on 2-deoxyglucose, and selection of colonies with large clear zones on iodine-stained glucose-starch agar plates. Amylases were produced in both wild-type and mutant strains when starch was added to cells growing on xylose but not when starch was added to cells growing on glucose. In both wild-type and mutant strains, glucoamylase and pullulanase were produced at high levels in starch-limited chemostats but not in glucose- or xylose-limited chemostats. Therefore, we concluded that amylase synthesis in C. thermohydrosulfuricum was inducible and subject to catabolite repression. The mutants produced about twofold more glucoamylase and pullulanase, and they were catabolite repression resistant for production of glucose isomerase, lactase, and isomaltase. The mutants displayed improved starch metabolism features in terms of enhanced rates of growth, ethanol production, and starch consumption.
 ...
PMID:Regulation and genetic enhancement of glucoamylase and pullulanase production in Clostridium thermohydrosulfuricum. 393 38

In adult sparse-fur mutant mice, ornithine transcarbamylase (OTC) activity represents only 14% of the normal values. We studied the development of this activity from birth to adult period and demonstrated that the enzyme deficiency is already fully expressed at birth, in both the liver and the small intestine of mutants. Since OTC catalyzes the conversion of ornithine to citrulline, in the presence of carbamoyl-phosphate, the effect of a disturbed ornithine metabolism on the postnatal development of the small intestine has been evaluated. The normal appearance of sucrase as well as the normal increase of glucoamylase, trehalase, and alkaline phosphatase activities are delayed in sparse-fur mice compared with controls. Moreover, normal adult values are never attained. In contrast, the normal decline of lactase activity is impaired while leucylnaphthylamidase activity is unaffected. Cell proliferation, as evaluated by [3H]thymidine incorporation into DNA and mitotic index, is less active during the 3rd wk of life in mutants. These phenomena are closely associated with a transient weak arginase and ornithine decarboxylase activity in the small intestine. Since arginase catalyzes the conversion of arginine to orthithine, thus ensuring the availability of this substrate for ornithine decarboxylase activity, these results indicate a disturbance of polyamine metabolism in mutant enterocytes with a consequent delay in postnatal differentiation and proliferation. Sparse-fur mutant mouse may therefore represent a useful animal model for evaluating the role of ornithine metabolism in the maturation process of the small intestine.
 ...
PMID:Postnatal maturation of enterocytes in sparse-fur mutant mice. 395 97

Human fetal intestine (10-14 wk gestation) has been cultured as explants in a serum-free Leibovitz L-15 medium for periods up to 9 days. As determined by light microscopy, the overall architecture of the intestinal explant was maintained throughout the culture period. At the ultrastructural level the villus absorptive cells remained tall with well-defined brush border, apical tubular system, and supranuclear and infranuclear accumulations of glycogen. All other epithelial cell types were also preserved. The incorporation of [3H]thymidine and [3H]leucine continued during the culture period, reflecting a sustained synthesis of deoxyribonucleic acid and proteins. The hydrolytic activities of the brush border membrane were established based on data obtained throughout the course of the culture of a large number of intestinal specimens. Sucrase, maltase, glucoamylase, trehalase, lactase, alkaline phosphatase, and gamma-glutamyl transpeptidase activities increased during the 9 days of culture even though different patterns were recorded. These observations clearly established that human fetal small intestine can be maintained in organ culture for at least 9 days in a serum-free medium.
 ...
PMID:Explant culture of human fetal small intestine. 396 5

The influence of two new 1-desoxynojirimycin derivatives, BAY m 1099 and BAY o 1248, on rat small intestinal disaccharidases (sucrase, maltase, isomaltase, glucoamylase, lactase, trehalase) and alkaline phosphatase activity has been investigated in vitro. Both compounds are very potent alpha-glucosidase inhibitors. Tested in the range of 0.1-5.0 micrograms/ml, inhibition is strongest on sucrase (up to 97.1%) and glucoamylase (up to 96.7%). BAY m 1099 also reduced (up to 56.4%) beta-galactosidase (lactase) activity. For both inhibitors a competitive type of sucrase inhibition was demonstrated (Lineweaver-Burk plot). Affinity versus sucrase was unusually tight. The Ki of BAY m 1099 versus sucrase amounted to 1.14 x 10(-7) M and of BAY o 1248 to 6.92 X 10(-8) M (Dixon plot). Both inhibitors did not impair active transport of L-leucine or methyl-alpha-D-glucoside into everted rings of rat jejunum in vitro.
 ...
PMID:Effect of 1-desoxynojirimycin derivatives on small intestinal disaccharidase activities and on active transport in vitro. 403 92

The influence of hydrocortisone on the differentiation and proliferation of human fetal small intestine was studied. Fetal intestine (12- to 14-week gestation) was cultured during 5 days at 37 degrees C in serum-free Leibovitz L-15 medium alone or supplemented with hydrocortisone (12.5, 25, and 50 ng/ml). The addition of different concentrations of hormone did not affect the morphology of the intestinal explants. Brush border membrane hydrolytic activities, namely, sucrase, lactase, glucoamylase, trehalase, and alkaline phosphatase activities, were assayed in the intestinal tissue. A specific increase of lactase and alkaline phosphatase activities was induced by the addition of 25 and 50 ng hydrocortisone/ml culture medium. The DNA synthesis evaluated by the incorporation of [3H]thymidine was increased by the addition of 50 ng hydrocortisone/ml. The sites of incorporation into the different layers of the intestinal wall were studied by radioautography. The incorporation of the radioactive precursor occurred mainly in the epithelium and to a lesser degree in the mesenchyme and muscular layers. Labeled epithelial nuclei were located in the intervillous areas and developing crypts but not on the villi. The addition of hydrocortisone induced a significant increase of the labeling index of the epithelial cells. The present work provided for the first time some basic data on the influence of hydrocortisone on brush border hydrolytic activities and on epithelial cell proliferation of human fetal small intestine.
 ...
PMID:Influence of hydrocortisone on human fetal small intestine in organ culture. 406 77

The influence of hydrocortisone (10(-8)--10(-5) M) and thyroxine (10 (-9)--10(-6) M) on intestinal epithelial cell differentiation and proliferation have been studied using explants of suckling mouse jejunum maintained in serum-free organ culture. Hydrocortisone induced the appearance of sucrase activity and increased trehalase, glucoamylase, lactase and alkaline phosphatase activities. Thyroxine was completely ineffective at all the concentrations used. None of these hormones affected the mitotic activity or the 3H-thymidine incorporation into DNA. These results demonstrate that hydrocortisone but not thyroxine acts directly on intestinal brush border membrane differentiation and that both hormones do not influence the proliferation of the epithelial cells during postnatal development.
 ...
PMID:Comparative study of the effect of hydrocortisone and thyroxine on suckling mouse small intestine in organ culture. 614 44

Explants of suckling mouse jejunum have been maintained in serum-free organ culture with or without insulin added to the medium in order to determine the possible direct effect of this hormone on the hydrolytic functions of the brush border and on the proliferation of the crypt cells. The addition of insulin induced the precocious appearance of sucrase activity and increased trehalase, glucoamylase and lactase activities. Alkaline phosphatase activity remained unaffected in the tissue as well as in the medium. An increased DNA content and 3H-thymidine incorporation into DNA were already recorded after 24 h of culture. The mitotic index was significantly increased after 24 h and remained elevated when the culture was extended to 48 h. These results show that insulin directly influences the enzymatic maturation and the proliferation of intestinal epithelial cells of suckling mouse.
 ...
PMID:Insulin influences the maturation and proliferation of suckling mouse intestinal mucosa in serum-free organ culture. 639 67

The longitudinal distribution of the main brush border membrane hydrolases was studied in six entire human small intestine, one of which was found to be lactase-deficient. Sucrase and lactase activities were found to be highest in the jejunum, whereas glucoamylase activity rose steadily and reached its highest activity near the ileocecal valve. Maltase activity distribution was intermediate between that of sucrase and of glucoamylase. Neutral aminopeptidase, acid aminopeptidase and dipeptidyl peptidase IV activities tended to increase toward the end of the small bowel, the latter two activities rising more than the first one. Furthermore, the protein compositions of the brush border membrane in the jejunum and in the ileum were compared after electrophoresis on polyacrylamide gels and crossed-immunoelectrophoresis; protein patterns were found to be similar along the gut, and enzyme-specific activities varied in parallel with the amounts of their corresponding proteins. In the lactase-deficient intestine, the protein band corresponding to lactase was not visible. Maximal digestive capacity was thus localized in the jejunum only for disaccharides, and in the ileum for the more complex substrates, oligosaccharides, and peptides; this finding suggests that the ileum may play a greater role in their terminal digestion than is usually admitted.
 ...
PMID:Longitudinal study of the human intestinal brush border membrane proteins. Distribution of the main disaccharidases and peptidases. 641 75

Activities of several carbohydrases and peptidases were determined in proximal, middle, and distal thirds of the jejunoileum of female 16-wk-old rats that were fed a high-starch (70 cal%), low-fat (7 cal%) diet for 2 wk and also in rats that (after this introductory period) were fed an isocaloric low-starch (5 cal%), high-fat (73 cal%) diet for 1, 2, and 3 days. The body weight changes, food intake, amount of protein per intestinal segment, and rate of enterocyte migration were practically the same in all groups during these experimental periods. The decreased intake of starch was followed by a rapid decrease (40-80%) of carbohydrases (lactase, sucrase, maltase, and glucoamylase) within the first 24 h in total intestinal homogenates--and as studied in cryostat serial sections--in all regions of the jejunal villus-crypt columns, and mainly in proximal and middle segments. In contrast, the activities of leucylnaphthylamidase and L-phenylalanylglycine hydrolase exhibited little change except for a slight temporary decrease of activity on the 1st day in the proximal segment only (25-30%). Thus these data show that a decrease of starch content in an isocaloric diet evokes a rapid decrease in the activity of microvillar carbohydrases and that activity of these enzymes both in mature and immature enterocytes is capable of reacting to a change (decrease) of dietary carbohydrate content.
 ...
PMID:Dietary-induced rapid decrease of microvillar carbohydrase activity in rat jejunoileum. 661 86

The development of glucoamylase activity was compared to that of disaccharidase in the small intestinal mucosa of infants and children. By the age of one month, infants have glucoamylase and disaccharidase levels comparable to those of young adults, indicating that young infants may be able to digest and absorb starches. In infants and children with varying degrees of mucosal injury of the small intestine, the activities of glucoamylase decreased progressively with increasing severity of the villus atrophy. However, the reduction of lactase, palatinase, and sucrase activities was more severe than the loss of activities of glucoamylase and maltase. Thus, children and infants may tolerate polymers of glucose better than disaccharides when they have mucosal injury associated with prolonged diarrhea.
 ...
PMID:Glucoamylase and disaccharidase activities in normal subjects and in patients with mucosal injury of the small intestine. 677 72


<< Previous 1 2 3 4 5 6 7 8 9 Next >>