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)

Rotaviruses are now regarded as important causes of diarrhoea in man, cattle, pigs, mice, and possibly other animals. Characteristically, disease occurs in newborn and young animals, and infection seems limited to the differentiated gut epithelial cells. The major surface polypeptide of the calf scours rotavirus is glycosylated, and highly purified beta-galactosidase (lactase) interacts with the virus in vitro causing removal of the outer shell of the capsid (uncoating). It is suggested that lactase present in the brush border of the intestinal epithelial cell performs a similar function in vivo by acting as a combined receptor and uncoating enzyme for the rotavirus. This hypothesis is consistent with the observations that rotaviruses seem to infect only gut epithelial cells, and that infant animals, whose lactase concentrations are generally higher than those of adult animals, seem more susceptible to rotavirus infections. Implications of the hypothesis include possible new approaches to laboratory cultivation of rotaviruses, which should be more successful in cells selected for surface lactase activity, and the suggestion that the epidemiology of human rotavirus infections may be influenced by the fact that different ethnic groups have different lactase levels (and hence lactose intolerance) in adulthood.
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PMID:Is lactase the receptor and uncoating enzyme for infantile enteritis (rota) viruses? 5 21

The purpose of this study was to determine whether the developmental decline in lactase specific activity (mumol/min/g protein) in the rat was associated with (a) changes in the relative quantities of immunoisolated precursor and mature forms of the enzyme purified by SDS-PAGE and/or (b) immunohistologic changes in the jejunal mucosa. We studied 10- and 16-day-old suckling rat pups, 22-day-old weaned rat pups, and adult female rats (nongravid, pregnant, and lactating). Lactase activity was three- to fourfold higher in 10-day-old pups than in adult rats. Lactase activity was 27% greater in lactating compared with nongravid or pregnant rats. Three molecular forms of the enzyme that migrated identically in all animals were observed on SDS-polyacrylamide gels stained with Coomassie blue: 140-kDa (mature brush border form), 200-kDa, and 220-kDa (apparent precursor forms). There was a striking difference in the proportions of the three polypeptides at different ages that was unrelated to animal status, i.e., pregnant or lactating. As the animals aged, the relative amount of the 140-kDa band declined from 86 +/- 1.1% of the total immunoprecipitated lactase in 10-day old suckling pups to 68 +/- 0.7% in adults. Simultaneously, the relative concentration of the 200-kDa band rose from 1.7 +/- 0.4% in the 10-day-old to 19 +/- 0.6% in adults. The relative concentration of the 220-kDa polypeptide did not change as a function of age.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Developmental changes in lactase-phlorizin hydrolase precursor isoforms in the rat. 143 63

The 225 kDa precursor of intestinal lactase-phlorizin hydrolase (LPH) consists of four tandemly-organized homologous domains flanked by a signal peptide at the N-end and by a transmembrane anchor at the C-end of the polypeptide chain. While the mature LPH of 130 kDa has already been shown to originate from the C-half of the precursor, no protein deriving from the N-half has been identified so far. Using monospecific antibodies raised against the mature LPH or against a recombinant protein containing the sequence of the N-end of the LPH precursor, we have searched for co-translated protein(s) of LPH in enterocytes and in the intestinal lumen of suckling rats. Since no additional protein to LPH was revealed by these antibodies, it is suggested that the polypeptide chain corresponding to the N-half of the LPH precursor undergoes rapid turnover.
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PMID:Do co-translated product(s) of lactase-phlorizin hydrolase accumulate in the rat intestine? 147 99

Insulin, found in human and pig colostrum and mature milk, appears to influence small intestinal growth and development. Ileal lactase activity is increased when porcine insulin is added to feedings administered to newborn piglets. We studied 2-day-old miniature piglets to determine whether the increase in lactase activity is accompanied by changes in enterocyte expression of lactase activity, steady-state levels of lactase mRNA, and/or posttranscriptional changes in lactase processing. We randomized the piglets to receive bottle feedings of a swine-weaning milk formula with (group F + I) or without (group F) the addition of 85 mU/ml of regular porcine insulin. The piglets were fed for 6 days (to 8 days of age), after which they were killed and the small intestine removed for analysis. Despite large differences between groups in enterocyte expression of lactase activity in the ileum, no differences were noted in the level of ileal lactase mRNA. The relative proportions of the 207, 210, and 230 kDa precursors of the 160 kDa mature lactase protein were similar between groups. These data indicate that the insulin-induced increased expression of ileal lactase activity is not regulated at the level of its mRNA or at the level of processing of the polypeptide.
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PMID:Effect of oral insulin on lactase activity, mRNA, and posttranscriptional processing in the newborn pig. 159 71

Intracellular processing of human intestinal lactase-phlorizin hydrolase (LPH) includes an essential proteolytic cleavage step that generates the mature brush border enzyme from the single-chain polypeptide precursor (pro-LPH). Previous work in organ culture of small intestinal biopsy samples [Naim, Sterchi & Lentze (1987) Biochem. J. 241, 427-434] has demonstrated that this cleavage occurs intracellularly. Since no intermediate forms of pro-LPH (trimmed or complex glycosylated) could be discerned in pulse-chase analyses it was suggested that the cleavage process occurs at a fast rate. To identify intermediate forms of pro-LPH prior to cleavage, I studied the biosynthesis of LPH by employing a pulse-chase protocol in mucosa explants (or biopsies) at reduced temperatures (22 degrees C). Here, I could identify by immunoprecipitation with monoclonal anti-LPH antibodies four LPH forms that exhibited a product-precursor relationship:mannose-rich precursor (pro-LPHh), trimmed pro-LPH (LPHt), complex glycosylated pro-LPH (pro-LPHc) and cleaved, mature LPH (LPHm). The results clearly indicate that the generation of mature LPH is preceded by complex glycosylation of the precursor form. The fact that this was not previously observed in the same experimental system under normal biosynthetic labelling conditions (37 degrees C) demonstrates that the cleavage process of pro-LPH occurs at a fast rate in the human small intestine.
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PMID:Processing of human pro-lactase-phlorizin hydrolase at reduced temperatures: cleavage is preceded by complex glycosylation. 163 91

The intestinal sucrase-isomaltase precursor is cleaved at the brush border membrane by luminal proteases. Whether the lactase precursor also is cleaved by luminal proteases is uncertain. Lactase synthesis and processing was studied in 0- and 15-day-old rats after IP administration of [35S]methionine, and changes in precociously cortisone-induced sucrase-isomaltase were used as an internal control. Mucosal lactase and sucrase-isomaltase were separately immunoprecipitated and analyzed by autoradiography after electrophoresis. In both 0- and 15-day-old rats, mucosal lactase appeared as a 200K lactase precursor band at 30 minutes and as 200K and 225K lactase precursor bands at 60 minutes and was cleaved to form a 130K lactase band 120-240 minutes after labeling; sucrase-isomaltase similarly appeared as 210K and 220K bands at 30-60 minutes and was cleaved to form 140K I and 120K S subunits by 240 minutes in day 15 rats. To determine the role of luminal proteases, intestinal segments were isolated in situ and the luminal contents were flushed 30 minutes after labeling. Unflushed segments were used as controls. Only lactase precursor and sucrase-isomaltase precursor were present 240 minutes after labeling in flushed intestinal segments, but lactase precursor and sucrase-isomaltase precursor were cleaved in unflushed segments. Addition of trypsin or elastase into the lumen of flushed segments resulted in partial cleavage of lactase precursor but not of sucrase-isomaltase precursor. Luminal contents collected from the small intestine of day 15 rats 120 and 240 minutes after labeling showed 35S-labeled 130K and 80K polypeptides in lactase immunoprecipitates. It is concluded that intestinal lactase is synthesized as lactase precursor and transported to brush border membrane and cleaved by luminal proteases, and the amino end polypeptide cleaved from lactase precursor is released into the lumen.
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PMID:Posttranslational cleavage of rat intestinal lactase occurs at the luminal side of the brush border membrane. 190 27

We have described the methods used for studying the biosynthesis and the post-translational processing of sucrase-isomaltase (SI), lactase-phlorizin hydrolase (LPH) and maltase-glucoamylase (MGA) in human small intestinal mucosa. Our results are discussed in the context of findings by other researchers. A surprising finding coming out of all these studies is that SI, LPH and MGA are structurally quite different. SI and LPH are both synthesized as large molecular weight precursors which are proteolytically processed to the mature enzymes. In the case of SI, this processing occurs after insertion of the precursor into the brush border membrane and is catalysed by pancreatic proteases; the mature form consists of the two subunits sucrase and isomaltase, the latter containing an N-terminal peptide anchor. Proteolytic processing of the LPH-precursor occurs intracellularly, yielding a mature enzyme in the form of a two active site polypeptide which is anchored via a C-terminal peptide. The role of the large cleaved propolypeptide of LPH is not yet known. MGA is the largest of the three disaccharidases, having a molecular weight of greater than 300 kDa. No proteolytic processing seems to be taking place during biogenesis of MGA in human mucosa, and the mode of attachment to the membrane is unknown at present. The application of the methods described to the investigation of congenital sucrase-isomaltase deficiency (CSID) and lactase restriction in adults is presented and differences between CSID and LPH restriction are discussed.
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PMID:Molecular aspects of disaccharidase deficiencies. 211 33

We report the primary structures of human and rabbit brush border membrane beta-glycosidase complexes (pre-pro-lactase-phlorizin hydrolase, or pre-pro-LPH, EC 3.2.1.23-62), as deduced from cDNA sequences. The human and rabbit primary translation products contain 1927 and 1926 amino acids respectively. Based on the data, as well as on peptide sequences and further biochemical data, we conclude that the proteins comprise five domains: (i) a cleaved signal sequence of 19 amino acids; (ii) a large 'pro' portion of 847 amino acids (rabbit), none of which appears in mature, membrane-bound LPH; (iii) the mature LPH, which contains both the lactase and phlorizin hydrolase activities in a single polypeptide chain; (iv) a membrane-spanning hydrophobic segment near the carboxy terminus, which serves as membrane anchor; and (v) a short hydrophilic segment at the carboxy terminus, which must be cytosolic (i.e. the protein has an Nout-Cin orientation). The genes have a 4-fold internal homology, suggesting that they evolved by two cycles of partial gene duplication. This repetition also implies that parts of the 'pro' portion are very similar to parts of mature LPH, and hence that the 'pro' portion may be a water-soluble beta-glycosidase with another cellular location than LPH. Our results have implications for the decline of LPH after weaning and for human adult-type alactasia, and for the evolutionary history of LPH.
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PMID:Complete primary structure of human and rabbit lactase-phlorizin hydrolase: implications for biosynthesis, membrane anchoring and evolution of the enzyme. 246 Mar 43

The biosynthesis and maturation of the human intestinal lactase-phlorizin hydrolase (LPH; EC 3.2.1.23-3.2.1.62) has been studied in cultured intestinal biopsies and mucosal explants. Short time pulse labelling revealed on high mannose intermediate of Mr 215,000 which was converted upon endo-beta-N-acetylglucosaminidase H (endo-H) digestion to a polypeptide of Mr 200,000. The brush border form of LPH was revealed after longer pulse periods and has Mr 160,000. It possesses mainly complex oligosaccharide chains and, owing to its partial endo-H sensitivity, at least one chain of the high mannose type. Leupeptin partially inhibited the appearance of the Mr-160,000 polypeptide. Monensin treatment of biopsies resulted in the modification of the Mr-160,000 species to the Mr-140,000 molecule, which was endo-H sensitive. Pulse-chase analysis indicated a slow post-translational processing of the high mannose precursor (Mr 215,000) to yield the mature brush-border form (Mr 160,000) of LPH. Our results further indicate that LPH is synthesized as a single polypeptide precursor which is intracellularly cleaved to yield the mature brush border of LPH. The data presented suggest that this cleavage occurs during the translocation of the molecule across the Golgi complex.
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PMID:Biosynthesis and maturation of lactase-phlorizin hydrolase in the human small intestinal epithelial cells. 310 75

The adult guinea-pig small intestinal microvillus membrane was purified approximately 25-fold by both cation-precipitation and differential centrifugation methods. Comparison by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed no substantial differences in polypeptide composition between the two preparations. One-dimensional SDS-PAGE and two-dimensional isoelectric focussing (IEF)/SDS-PAGE, together with Coomassie-blue, silver and lectin-staining, showed three major high molecular weight polypeptides, Mr 108 000, 116 000 and 127 000, as well as a 47 kDa protein (actin), as major constituents of the membrane. The proteins of Mr 108 000 and 116 000 were strongly concanavalin A reactive. A detailed two-dimensional IEF/SDS-PAGE map of the membrane was constructed. Sodium carbonate treatment showed the two concanavalin A-reactive glycoproteins, Mr 108 000 and 116 000, comprising the sucrase-isomaltase complex, to be loosely-associated 'extrinsic' microvillus membrane proteins. Two proteins, Mr 127 000 and 135 000, were tightly-associated 'intrinsic' microvillus proteins. Despite regional differences in specific activity of some small intestinal microvillar enzymes, most noticeably enterokinase (EC 3.4.21.9) and dipeptidyl peptidase IV (EC 3.4.14.x), no substantial regional differences were seen in microvillus membrane polypeptide composition. In contrast, a substantial increase in the major high molecular weight proteins of Mr 108 000 and 116 000 accompanied a 10-fold rise in sucrase-isomaltase activity, and loss of a major protein of Mr 131 000 accompanied the complete loss of lactase activity from the membrane during postnatal development.
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PMID:Two-dimensional isoelectric focussing/sodium dodecyl sulphate polyacrylamide gel electrophoretic mapping and some molecular characteristics of the proteins of the adult guinea-pig small intestinal microvillus membrane. 399 21


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