Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.26 (invertase)
 4,927 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have isolated a cDNA (cNPK5) that encodes a protein kinase of 511 amino acids from suspension cultures of tobacco cells. The predicted kinase domain of NPK5 is 65% identical in terms of amino acid sequence to that of the SNF1 serine/threonine protein kinase of Saccharomyces cerevisiae, which plays a central role in catabolite repression in yeast cells. SNF1 positively regulates transcription of various glucose-repressible genes of the yeast, such as the SUC2 gene for a secreted invertase, in response to glucose deprivation: snf1 mutants cannot utilize sucrose as a carbon source. Expression of cNPK5 in yeast cells allowed the snf1 mutant cells to utilize sucrose for growth and caused constitutive expression of the SUC2 gene in wild-type cells even in the presence of glucose, an indication that the NPK5 protein is present in a constitutively active form in S. cerevisiae. On the other hand, expression of cNPK5 failed to suppress the growth defect of the snf4 mutant cells in the presence of sucrose and to induce expression of the SUC2 gene. These results indicate that SNF4 is required for the induction of SUC2 expression by NPK5, as by SNF1, even if NPK5 is constitutively active in S. cerevisiae. The recombinant NPK5 protein is capable of autophosphorylation in vitro in a reaction that requires Mn2+ rather than Mg2+ ions but is inhibited by Ca2+ ions. Both dicotyledonous and monocotyledonous plants have several copies of the NPK5-related gene, which probably constitute a small gene family. NPK5-related genes were found to be expressed in the roots, leaves, and stems of tobacco plants. The high degree of structural conservation and the functional similarity of NPK5 to SNF1 lead us to speculate that NPK5 (or a related kinase) also plays a role in sugar metabolism in higher plants.
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PMID:Characterization of tobacco protein kinase NPK5, a homolog of Saccharomyces cerevisiae SNF1 that constitutively activates expression of the glucose-repressible SUC2 gene for a secreted invertase of S. cerevisiae. 816 54

The intestinal mucosa is characterized by cell proliferation, commitment, differentiation, digestion and absorption. These processes occur at specified locations along the crypt to villus axis. A technique is reported for the isolation of cells along this axis which allows the study of any one of these processes in an enriched population of cells. As an example, the uptake of transferrin-bound iron by enterocytes was studied. Rats were fed diets normal, high (30% carbonyl iron) or low in iron for 12 days. Cells from either the duodenum or ileum were isolated by incubating in a Ca(2+)-, Mg2+-free, cation chelating solution for varying periods. The incorporation of thymidine into DNA was measured in these cells as a marker of the crypt region, while alkaline phosphatase and sucrase activities marked mature enterocytes. The in vivo uptake of transferrin-bound 59Fe was measured in cells isolated either 2 or 4 h after intravenous injection. This procedure resulted in the isolation of 10 fractions of viable cells. Earlier fractions were enriched at least 10-fold in villus cells and the last fractions in crypt cells. Cells in intermediate fractions were at various stages of development. Uptake of transferrin-bound iron into enterocytes was highest with feeding an iron-loaded diet compared with control or iron-deficient diets. However, with all diets uptake was highest in crypt cells and this fell at the crypt-villus junction to be only 25%, as high at the villus tip as the crypt. A technique for the reproducible isolation of viable enterocytes along a crypt-villus axis is described. Transferrin receptor activity changes with maturation of the enterocyte.
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PMID:Characterization of isolated duodenal epithelial cells along a crypt-villus axis in rats fed diets with different iron content. 950 94

The sucrose operon of Clostridium beijerinckii NCIMB 8052 comprises four genes, which encode a sucrose-specific enzyme IIBC(Scr) protein of the phosphotransferase system (ScrA), a transcriptional repressor (ScrR), a sucrose hydrolase (ScrB) and an ATP-dependent fructokinase (ScrK). The scrARBK operon was cloned in Escherichia coli in three stages. Initial isolation was achieved by screening a C. beijerinckii genomic library in E. coli for clones able to utilize sucrose, while the remainder of the operon was isolated by inverse PCR and by plasmid rescue of flanking regions from a scrB mutant constructed by targeted gene disruption. Substrate specificity assays confirmed that the sucrose hydrolase was a beta-fructofuranosidase, able to hydrolyse sucrose and raffinose but not inulin or levans, and that the scrK gene encoded an ATP/Mg2+-dependent fructokinase. Both enzyme activities were induced by sucrose in C. beijerinckii. Disruption of the scr operon of C. beijerinckii by targeted plasmid integration into either the scrR or the scrB gene resulted in strains unable to utilize sucrose, indicating that this was the only inducible sucrose catabolic pathway in this organism. RNA analysis confirmed that the genes of the scr operon were co-transcribed on a 5 kb mRNA transcript and that transcription was induced by sucrose, but not by glucose, fructose, maltose or xylose. Primer extension experiments identified the transcriptional start site as lying 44 bp upstream of the scrA ATG start codon, immediately adjacent to the imperfect pelindrome sequence proposed to be a repressor binding site. Disruption of the scrR gene resulted in constitutive transcription of the upstream scrA gene, suggesting that ScrR encodes a transcriptional repressor which acts at the scrA operator sequence. The scrR gene is therefore itself negatively autoregulated as part of the polycistronic scrARBK mRNA
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PMID:The genes controlling sucrose utilization in Clostridium beijerinckii NCIMB 8052 constitute an operon. 1041 Dec 73

There is an overlap of carrier-mediated L-amino acid transport and apparent simple diffusion when measured in intestinal brush border membrane vesicles. Using L-threonine and L-glutamine as representative amino acids, this study was undertaken to estimate apparent simple diffusion of L-amino acids and to establish the effective dosage of HgCl2 for completely blocking carrier-mediated L-amino acid transport in porcine jejunal enterocyte brush border membrane vesicles. Jejunal mucosa was scraped from three pigs weighing 26 kg. Enterocyte brush border membrane vesicles, with an average enrichment of 24-fold in sucrase specific activity, were prepared by Mg2+-precipitation and differential centrifugation. In vitro uptake was measured by the fast filtration manual procedure. HgCl2 blocked the carrier-mediated initial transport of L-threonine and L-glutamine under Na+-gradient condition in a dose-dependent manner. At the minimal concentration of 0.165 micromol HgCl2 mg(-1) protein, carrier-mediated L-threonine and L-glutamine transport was completely inhibited. The apparent L-threonine and L-glutamine diffusion was estimated to be 8.6+/-0.7 and 12.4+/-1.0% of the total uptake at the substrate concentrations of 5 microM (L-threonine) and 50 microM (L-glutamine). Therefore, the treatment of porcine brush border membrane vesicles with a minimum of 0.165 micromol HgCl2 mg(-1) protein completely blocks carrier-mediated L-amino acid transport and enables the direct estimation of apparent L-amino acid diffusion in enterocyte brush border membrane vesicles.
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PMID:Estimation of apparent L-amino acid diffusion in porcine jejunal enterocyte brush border membrane vesicles. 1155 Nov 43

The objective of this study was to investigate the development of small intestinal size and digestive capacity of the jejunum in growing pigs. The weight, length, surface area, and mucosa weight of the small intestine were measured when pigs were 1, 3, 5, and 9 wk of age. Sucrase and alkaline phosphatase (ALP) activities of the jejunal brush-border membrane, prepared by differential centrifugation and Mg2+ precipitation, were determined at the respective postnatal stages. Body weights increased 7-fold from 2.7 kg at 1 wk to 23.32 kg at 9 wk postnatal. Body weight gains were greater (P < 0.05) from wk 3 to 5 than from wk 1 to 3. Weights of the small intestine and of the intestinal mucosa increased faster (P < 0.05) from 3 to 5 wk than from 1 to 3 wk; the slowest increase occurred from 5 to 9 wk. Weights of the duodenum, jejunum, and ileum, and mucosa from the respective sections increased (P < 0.05) as pigs grew from 3 to 9 wk. Mucosa weight relative to the weight of the section was greater (P < 0.05) for the duodenum and jejunum than for the ileum at 9 wk of age. Between the ages of 3 and 9 wk, the increase in mucosa weight was highest for the jejunum followed by the duodenum and the ileum. The increase was greatest for the duodenum followed by the jejunum and the ileum when mucosal weight was expressed per unit of appropriate intestinal section weight. There was a 55-fold increase in jejunal sucrase activity from 1 to 9 wk; the greatest rate of increase occurred between 5 and 9 wk. Total jejunal ALP activities in pigs at 9 wk was greater (P < 0.05) than at 5 wk, which in turn was greater than at 1 wk of age. In summary, increases in BW during the first 9 wk of postnatal growth in pigs are accompanied by significant developmental changes in digestive capacity including intestinal weights, length, and area as well as jejunal brush-border sucrase and ALP activities.
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PMID:Developmental changes in morphometry of the small intestine and jejunal sucrase activity during the first nine weeks of postnatal growth in pigs. 1636 97


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