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

Membrane-bound enzymes have certain specific differences compared with soluble enzymes. Membrane-binding often enables greater catalytic activity of associated enzymatic reactions, their regulation by low molecular weight substances (substrates and allosteric effectors, hormones) and compartmentation, etc. On the other hand, the binding of enzymes to membranes causes considerable difficulties as regards their isolation and the determination of their homogeneity and substrate specificity. Membrane enzymes provide a unique opportunity for studying the biogenesis of membranes and their physiological properties, however. These problems are discussed in relation to two types of membranes--the inner mitochondrial membrane and the membrane of the brush border of the small intestine. An example of the utilization of immunochemical methods is given in the results of a study of biosynthesis of the cytochrome oxidase complex in yeast cells. In the case of the brush border of the mammalian small intestine, the fact that certain enzymes, which are also of clinical significance from the aspect of congenital genetic defects, can be isolated only as complexes, constitutes a very real problem. This applies particularly to the sucrase-isomaltase complex and the lactase-beta-glucosidase complex. Solving questions of substrate specificity is of significance for the choice of a suitable analytical or histochemical method. The common regulation of these complexes gives an insight into the problems of membrane biogenesis, however. Immunochemical methods can be employed as sensitive criteria to support biochemical and morphological studies. Collaboration between the biochemist and histochemist proved especially valuable when determining the substrate specificity of enzymes (glycosidases) in relation to histochemical substrates, when applying histochemical methods for detecting enzymatic activity in immunoprecipitates and acrylamide gels and in immunohistochemical studies of the localization and developmental differentiation of the enzymes of the brush border of the small intestine.
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PMID:Biochemistry and immunochemistry of membrane-bound enzymes. 9 30

A method for the histochemical demonstration of "hetero-beta-galactosidase" was elaborated. The enzyme is demonstrated in cryostat sections by the semipermeable membrane technique. Pairs of membranes--one pre-washed in saline--are used. The most sensitive method is post-coupling demonstration with 6-Br-2-naphthyl-beta-D-glucoside. The incubation time must be short, to avoid diffusion. The method allows cellular localization. The method with alpha-naphthyl-beta-D-glucoside and hexazonium-p-rosaniline is less sensitive, but localization is better. Indigogenic methods are the least sensitive. The enzyme is localized in the supranuclear zone of differentiated enterocytes of the human, monkey and rabbit small intestine, with maximum activity in the jejunum. The activity of the enzyme is low in patients with coeliac sprue, in the active phase of the disease. In isolated lactase deficiency it is normal. In the kidney, the enzyme is localized chiefly in the cytoplasm of the proximal tubule cells.
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PMID:Demonstration of "hetero-beta-galactosidase" "in situ". 9 37

Part of the digestive flora in the adaptation to lactose consumption. Lactase activity was determined with adult Wistar rats. Some of which were accustomed to lactose since weaning. For this purpose, the tissue of jejunum, the flora of the ileum, the caecum and the large intestine were examined. When the rats received a high lactose diet, the lactase of the jejunum is more active because of both the intestinal tissue development and a higher production of enzyme by protein unit. But the main source of lactase is the digestive flora of the animal: a lactase flora develops in the ileum, the large intestine and mainly the caecum. The caecum lactase represents about half of the total lactase activity. The flora of the animal which has not consumed lactose since weaning can develop a noticeable lactase activity after 7 hr of incubation in presence of lactose. It is also the caecum flora which shows the greatest capacity of adaptation to lactose.
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PMID:[Role of the digestive flora in adaptation to lactose consumption in rats]. 9 89

After bypass operation for obesity the remaining lactose-hydrolyzing capacity of the functioning shunt is very low, especially if the shunt is constructed from a shorter jejunal and a longer ileal segment. In most cases a temporary decrease in the lactase activity of the jejunal part of the shunt occurs during the first postoperative months. In the present study lactose provoked or aggravated diarrhoea and other symptoms in 20 of 33 shunt-operated patients, and 10 patients reported milk intolerance postoperatively. Oral glucose tolerance tests indicated that the lactase activity was rate limiting for lactose absorption postoperatively.
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PMID:Lactose malabsorption after bypass operation for obesity. 9 6

A considerable increase occurs in D-glucose uptake and brush border sucrase and lactase activities in the intestine of monkeys treated with a single oral dose of DDT. Brush border alkaline phosphatase activity remains unaffected in the pesticide treated animals. In vitro addiction of DDT has no effect on the sugar absorption and disaccharidase activities.
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PMID:Effects of DDT (chlorophenotane) administration on glucose uptake and brush border enzymes in monkey intestine. 9 80

Studies were undertaken to determine the relationship of intestinal disaccharidase activity to age and race, and the relationship of mucosal damage to a primary low lactase activity. The first study consisted of data on 399 persons (339 whites, 53 blacks, and 7 American Indians) ages 1 month to 93 years, with normal intestinal histology. Among whites, all 117 children 5 years old or under had high lactase levels, whereas low levels were found only in subjects over 5 years of age. No low lactase levels were identified among the 11 black children 3 years old or under, but in comparison to coetaneous white children, their mean lactase activity was signficantly less. The majority of older blacks had low lactases. In whites and blacks alpha-disaccharidases did not participate in the age-related changes demonstrated with lactase. Of the 7 American Indians, none under 26 months old had low lactase levels, whereas the 4 over 10 years old had low activities. Heterozygotes for sucrase-isomaltase deficiency were identified only among whites. Low lactase levels developed during childhood in all races studied, however, many for unknown reasons maintained their lactose tolerance until adulthood. In the second study of 13 additional children with secondary disaccharidase deficiencies, emergence of a primary low lactase was related to age and race, rather than to mucosal damage. It appears that primary low intestinal lactase levels are absent or rare in whites under 5 and blacks under 3 years of age, and the deficiency is not related to mucosal damage.
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PMID:Intestinal disaccharidase activities in relation to age, race, and mucosal damage. 10 Mar 68

Screening for cystic fibrosis (CF) in newborns is desirable, and efforts should continue in establishing a system of easily available, reliable, simple, and inexpensive tests. In addition to the Boehringer-Mannheim (BM) test for the detection of albumin, we propose the assay for lactase and beta-D-fucosidase in meconium. These latter two enzymes are present in the meconium of babies with CF and absent in meconium of most healthy babies. In a mass screening program for CF involving 20,182 specimens of meconium using only the BM strip, we found 46 positive results. Twenty-nine specimens came from infants with CF, six of whom had meconium ileus. Seventeen specimens yielded false-positive results by the BM test. Eleven of these would have been excluded by the addition of the lactase and beta-D-fucoside assay, thus reducing the false-positive test results by nearly 61%. In a comparative study of the three methods, the lactase and beta-D-fucosidase yielded 1.2% false-positives when examined independently. Performance of these two assays may allow greater specificity in diagnosis when used in addition to the BM test.
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PMID:Studies in meconium. An approach to screening tests to detect cystic fibrosis. 10 86

A sensitive protein-binding assay has been used to measure plasma concentrations of total corticosterone during postnatal development in the rat. These concentrations were extremely low on days 6--12, showed a significant rise by day 14, and then continued to rise until peaking on day 24. Plasma titers of corticosteroid-binding globulin rose even more dramatically from day 12 onward. Consequently, the percentage of total plasma corticosterone, which was protein-bound, showed a gradual rise from 78% on day 12 to 98% on day 24. Despite this trend, when concentrations of free corticosterone were calculated, they were found to have a developmental profile very similar to that of total corticosterone. Assay of jejunal lactase and sucrase in the same animals that were used for the corticosterone studies showed that the ontogenic rise of both total and free corticosterone preceded the developmental changes in the activities of these enzymes by approximately 2 days. The data suggest that the rise in free corticosterone that begins on day 14 acts as a cue for enzymic changes in both liver and intestine.
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PMID:Plasma concentrations of total and free corticosterone during development in the rat. 10 38

Starvation overnight and starvation for 48 h reduced the weight and the protein content of mucosal scrapings, but only minimally reduced the DNA content of the mucosal scrapings. The activity of sucrase and maltase was reduced by both periods of starvation. The activity of lactase and of acid and alkaline phosphatase, however, was less subject to starvation. There were striking differences in the response to starvation between the proximal, mid and distal third of the small intestine. The importance of the proper reference system was discussed.
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PMID:Effect of starvation on small intestinal enzyme activity in germ-free rats. 10 66

Using freeze-dried or sections from fresh-frozen or aldehyde-fixed material nitro BT (NBT), tetranito BT (TNBT), distyryl nitro BT (DS-NBT), thiocarbamyl nitro BT (TC-NBT) or benzothiazolylstyrylphthalhydrazidyl tetrazolium chloride (BSPT) were tested as auxiliary reagents for the localization of glycosidases, phosphatases and non-specific esterases with indoxyl substrates in rat tissues. By means of NBT or TNBT as a tetrazolium salt acid beta-D-galactosidase, beta-D-N-acetylglucosaminidase, acid phosphatase, neuraminidase and non-specific esterase can only be localized at the cellular level; a more precise localization is possible for lactase-beta-D-glucosidase in the intestinal brush border, and the best results are obtained in the demonstration of alkaline phosphatase; among all methods described previously the tetrazolium procedure with TNBT is the method of choice for the light microscopic localization of this enzyme. Reverse data are observed with BSPT as a tetrazolium salt; then, all acid and neutral hydrolases can be exactly localized in lysosomes, secretion granules, cytoplasm and/or microvilli of many cells and tissues provided BSPT-formazan is stabilized by osmification. Furthermore, this procedure enables the reliable ultracytochemical demonstration of these enzymes. However, in the case of alkaline phosphatase only sites with high enzyme activity reveal a positive reaction. -DS- and TC-NBT are inferior to NBT, TNBT or BSPT.
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PMID:[Tetrazolium methods for the histochemical investigation of hydrolases (author's transl)]. 10 69


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