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)

Lactase and maltase, the predominant sugar hydrolases associated with the intestinal brush bordermembrane of the suckling rat, were purified essentially free of the other to near homogeneity (lactase at specific activity 23, maltase at specific activity 58), and their specific physiocochemical properties determined. Antisera prepared to each showed by immunodiffusion a single common precipitin line with pure enzyme and solubilized proteins of the brush border membrane. Brush border membranes were purified 26--35-fold from infant rat intestine. Membranes prepared from 10-day-old rats contained 32% protein, 43% lipid and 25% carbohydrate with lactase and maltase estimated to comprise in excess of 10% and 2%, respectively, of the membrane protein. Immunotitration curves of lactase and maltase showed equivalent antibody binding by the membrane-bound and free enzyme forms. Furthermore, antibody binding to one enzyme did not affect the immunotitration curve or the extractability (by papain or Triton X-100) of the other membrane-bound enzyme. It was concluded that the lactase and maltase molecules are attached singly on the external membrane surface in a spatially independent manner with their antigenic sites as freely available to antibody binding as exhibited by their papain-solubilized counterparts.
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PMID:Sugar hydrolases of the infant rat intestine and their arrangement of the brush border membrane. 11 Mar 47

The arrangement of the sugar hydrolases, sucrase-isomaltase, maltase, and lactase on the microvillus membrane of rat intestine was investigated by immunological technique. The enzymes were purified essentially free of each other to near homogeneity and antisera of high specificity were obtained against each. Microvillus membranes were prepared routinely in high purity from rat intestine and contained an average 61% protein, 20% lipid, and 19% carbohydrate, with the sugar hydrolases comprising an estimated 20--25% of the membrane protein. The immunoreactivity of membrane-bound sucrase-isomaltase, maltase, and lactase was investigated with antisera demostrating specific reactivity to each, when tested in the presence of other membrane extractives. The membrane-bound enzymes were found in each case to combine with antibody in amounts equivalent to that required to effect precipitation of comparable units of the free enzymes from solution. Preloading membrane vesicles with antibodies to any two of the enzymes did not affect either the immunoreactivity or extractability (by papain or Triton X-100) of the third. The antibody-binding studies indicated an arrangement of these enzymes independent of each other on the membrane surface, in a manner allowing each to maintain a high degree of molecular freedom.
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PMID:Sugar hydrolases and their arrangement on the rat intestinal microvillus membrane. 11 6

The effect of methylglyoxal on protein -SH and -NH2 groups in cytosolic and membranous fractions of epithelial cells lining the gastrointestinal tract of rat was investigated, using isolated villus and crypt cells (enterocytes) and colonocytes. It was found that 11-12% cytosolic protein -SH and 14-17% membrane protein -SH groups were lost when villus and crypt cells were treated with 2 mM methylglyoxal. In colonocytes, the corresponding loss in protein -SH groups was 46 and 30% under the same treatment. Similarly, 27-37% protein -NH2 group in the cytosolic fraction and 18-19% protein -NH2 group in membranous fractions of the enterocytes were lost by 2 mM methylglyoxal treatment. In colonocytes, the loss of protein -NH2 group was 30 and 15% in cytosolic and membranous fractions, respectively, under the same treatment. Effect of methylglyoxal on activity of various brush border enzymes such as alkaline phosphatase, gamma-glutamyl transpeptidase, leucine aminopeptidase, Mg2(+)-ATPase, sucrase and lactase was also studied. Alkaline phosphatase and gamma-glutamyl transpeptidase activities were inhibited to the extent of 30 and 15% respectively. There was no significant change in the activities of other enzymes after treating the brush border vesicles with 2 mM methylglyoxal. These findings show that methylglyoxal can cause loss of protein thiol and amino groups and enzyme activity in mucosal cells of rat gastrointestinal tract and the effect is more pronounced in colonocytes, which are in constant contact with bacterial metabolites.
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PMID:Effect of methylglyoxal on protein thiol and amino groups in isolated rat enterocytes and colonocytes and activity of various brush border enzymes. 234 Nov 60

To elucidate the mechanism of the developmental decline in intestinal lactase activity at weaning, we examined lactase synthesis in suckling and adult rats. Lactase was purified to homogeneity from pooled intestines of newborn rats and used to raise a monospecific antibody. Using this antibody, we developed a quantitative immunoprecipitation assay for lactase. Intestinal microvillus membrane proteins were labeled in 15-day and adult rats by intraluminal pulse-chase with 3H-leucine, and newly synthesized lactase quantified by immunoprecipitation. When lactase synthesis was expressed as the quantity of microvillus membrane lactase synthesized relative to total microvillus membrane protein synthesized, a significantly greater proportion of 3H-leucine incorporation into lactase was demonstrated in the suckling animals. No structural differences between newly synthesized suckling and adult lactase were observed when they were compared by SDS-polyacrylamide gel electrophoresis and fluorography. These data suggest that a change in the rate of lactase synthesis plays a role in the postweaning decline in enzyme activity.
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PMID:Intestinal lactase synthesis during postnatal development in the rat. 393 Oct 41

Microvillus membrane vesicles from pig small intestine, isolated by hypotonic lysis, Mg2+ aggregation of contaminants and differential centrifugation, have been further purified by immunoadsorbent chromatography. The vesicles adhere to an immunoadsorbent prepared by coupling antibodies raised against three of the principal proteins of the brush border membrane (aminopeptidase, sucrase-isomaltase and lactase) to Sepharose 4B. After the contaminants are removed by washing, the adherent vesicles are released from the immunoabsorbent by applying shear forces. The purity of the immunoadsorbed vesicles has been established by electron microscopy and by measuring the activity of marker enzymes. The enrichment factor is 1.17 +/- 0.02 for aminopeptidase and 0.70 +/- 0.05 for 5'-nucleotidase. The contamination of the preparation before immunoadsorption constitutes 10% of the membrane protein and consists mainly of basolateral membrane fragments as judged from marker enzyme determinations and the lipid composition.
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PMID:Purification of microvillus membrane vesicles from pig small intestine by immunoadsorbent chromatography. 710 46

The effect of undernutrition during suckling has been investigated on the brush border enzymes and the intestinal uptake of D-glucose and glycine in rats at weaning. The brush border sucrase and alkaline phosphatase activities were drastically reduced, but lactase and leucine aminopeptidase levels were significantly elevated in the intestine of nutritionally deprived pups compared to controls. The uptake of D-glucose and glycine in undernourished rats was also augmented. The chemical composition of the brush border membrane analyzed in nutritionally deficient animals revealed an enhancement of the membrane protein, sialic acid, cholesterol, and phospholipids compared to the control group. [U-14C]D-Glucose incorporation into lipid constituents of the membrane suggested that the observed enhancement of the membrane lipids is the result of an increased synthesis in response to undernutrition.
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PMID:Intestinal brush border membrane structure and function: effect of early postnatal undernutrition. 725 34

Conscious unrestrained piglets were fasted overnight and infused intravenously with [2H3]leucine for 6 h. Sucrase isomaltase and lactase phlorizin hydrolase were immunoprecipitated from jejunal mucosal membranes, and the immunoprecipitates were electrophoresed on polyacrylamide gels. Bands corresponding to the pro and mature isoforms of both enzymes were acid hydrolyzed. [2H3]leucine isotopic enrichment was measured by gas chromatography-mass spectrometry using negative chemical ionization. Plasma leucine reached isotopic steady state within 90 min. The isotopic enrichment of mucosal leucine was 73% of that of plasma leucine. The high mannose and complex glycosylated forms of prolactase were in isotopic equilibrium, and their isotopic enrichment was 94% of mucosal leucine. The fractional synthesis rates of total and membrane protein were 0.45 and 0.65 days-1, whereas the processing rates of mature lactase, sucrase, and isomaltase were 0.90, 0.23, and 0.21 days-1, respectively. Approximately 65% of the label in the sucrase isomaltase immunoprecipitate was in the complex glycosylated precursor, whereas 73% of the label in lactase phlorizin hydrolase was in the mature (160 kDa) form. We conclude that the low rate of brush-border sucrase synthesis reflects a slow rate at which the complex glycosylated precursor is processed to the brush-border form.
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PMID:Brush-border disaccharidase synthesis in infant pigs measured in vivo with [2H3]leucine. 781 Jun 60

Polarized transport of proteins is contingent on the presence of specific protein structures or motifs that function as sorting signals. Our model protein to analyze and to identify such signals is that of lactase-phlorizin hydrolase (LPH), a strictly polarized brush border membrane protein of small intestinal epithelial cells. It is synthesized as a large pro-LPH precursor molecule, which is proteolytically processed to yield the mature brush border enzyme (LPHbeta). Pro-LPH as well as LPHbeta are correctly sorted to the brush border membrane. In this paper we examine the location of putative sorting signals in the pro-LPH molecule. Expression of a cDNA encoding the LPHbeta mature form in the absence of the LPHalpha species in Madin-Darby canine kidney (MDCK) cells reveal an LPHbeta molecule that is not as transport-competent as wild type pro-LPH. The proportion of complex glycosylated LPHbeta constitutes not more than 10% of the total synthesized protein. This form displays a similar trypsin sensitive pattern as wild type intestinal LPHbeta suggesting comparable folding patterns of the two species. Complex glycosylated LPHbeta is sorted to the apical membrane more efficiently than wild type pro-LPH. We conclude that the apical sorting signals for pro-LPH are exclusively found in the LPHbeta mature domain.
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PMID:The apical sorting of lactase-phlorizin hydrolase implicates sorting sequences found in the mature domain. 901 26

Structural and functional responses of the intestine to colostrum, milk replacer, oral electrolyte solution and food deprivation were examined during the first 6 h after birth in pigs. Total intestinal weight, surface area and mucosal mass were highest (P < 0.05) in pigs fed colostrum. The other diet groups did not differ, except that food-deprived pigs had lower surface area than the other groups. Feeding colostrum was associated with higher mucosal protein content (P < 0.05). Total intestinal brush border membrane protein content of pigs fed milk replacer, oral electrolyte solution and food-deprived pigs were 61, 44 and 56%, respectively, of those fed colostrum (P < 0.05). Pigs fed colostrum had higher total mucosal maltase activities than those that were food deprived, and total brush border membrane activities were higher than in those fed oral electrolyte solution. Total intestinal brush border membrane aminooligopeptidase activity was higher in pigs fed colostrum than in those given oral electrolyte solution or deprived of food, but total intestinal homogenate activities did not differ among groups. Diet influenced lactase activity only in the mid-region, and sucrase was not responsive to diet. Intestinal glucose transport capacity by intact intestinal tissues did not differ among diet groups. The ability of brush border membrane vesicles to actively accumulate glucose was lost when pigs were fed colostrum and milk replacer, but not when fed oral electrolyte solution or deprived of food. Our findings reveal how diet during the first 6 h after birth influences the structure and functional characteristics of the intestine. The responses vary between brush border membrane proteins and intestinal regions, and appear to differ from those described for older animals.
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PMID:Diet influences development of the pig (Sus scrofa) intestine during the first 6 hours after birth. 968 48

We have identified a novel mouse gene klph (Klotho-LPH related protein; where LPH stands for lactase-phlorizin hydrolase) that encodes a novel mammalian family 1 glycosidase-like protein. KLPH was a putative type I membrane protein that consists of N-terminal signal sequence, glycosidase domain, transmembrane region and short cytoplasmic tail. Despite its overall structural similarity to other family 1 glycosidases, the glutamic acid for the acid-base catalyst was not conserved in this protein. klph mRNA was predominantly expressed in the kidney and skin. Epitope-tagged KLPH was localized to the perinuclear tubular network structure of the endoplasmic reticulum in cultured cells.
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PMID:Identification of a novel mouse membrane-bound family 1 glycosidase-like protein, which carries an atypical active site structure. 1208 82


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