Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.31 (beta-glucuronidase)
 7,680 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The aim of the work described in this paper was to characterize the tubers of potato (Solanum tuberosum var. Prairie) plants that had been transformed with the Escherichia coli ADPglucose pyrophosphorylase (EC 2.7.7.27) gene, glgC-16, under the control of a patatin promoter. Over 30 lines of transformed plants with increased ADPglucose pyrophosphorylase activity were obtained. The tubers of six of these lines were compared with those of control plants expressing the gene for beta-glucuronidase. The average increase in pyrophosphorylase activity was 200%, and the highest was 400%. Western immunoblotting of tuber extracts showed that the amounts of glgC-16 protein were linearly related to the extractable activity of the ADPglucose pyrophosphorylase. Cell fractionation studies showed that the increased activity of the pyrophosphorylase in the glgC-16 tubers had a similar intracellular location, the amyloplast fraction, to that found in the control tubers. No pleiotropic changes in the maximum catalytic activities of the following enzymes could be detected in the glgC-16 tubers: sucrose synthase, fructokinase, UDPglucose pyrophosphorylase, phosphofructokinase, soluble starch synthase, starch branching enzyme, phosphoglucomutase and alkaline inorganic pyrophosphatase. The glgC-16 tubers are held to be suitable for the study of the role of ADPglucose pyrophosphorylase in the control of starch synthesis.
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PMID:Characterization of transgenic potato (Solanum tuberosum) tubers with increased ADPglucose pyrophosphorylase. 897 57

Plants possess two alternative biochemical pathways for sucrose (Suc) degradation. One involves hydrolysis by invertase followed by phosphorylation via hexokinase and fructokinase, and the other route-which is unique to plants-involves a UDP-dependent cleavage of Suc that is catalyzed by Suc synthase (SuSy). In the present work, we tested directly whether a bypass of the endogenous SuSy route by ectopic overexpression of invertase or Suc phosphorylase affects internal oxygen levels in growing tubers and whether this is responsible for their decreased starch content. (a) Oxygen tensions were lower within transgenic tubers than in wild-type tubers. Oxygen tensions decreased within the first 10 mm of tuber tissue, and this gradient was steeper in transgenic tubers. (b) Invertase-overexpressing tubers had higher activities of glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase, and alcohol dehydrogenase, and (c) higher levels of lactate. (d) Expression of a low-oxygen-sensitive Adh1-beta-glucuronidase reporter gene construct was more strongly induced in the invertase-overexpressing background compared with wild-type background. (e) Intact transgenic tubers had lower ATP to ADP ratios than the wild type. ATP to ADP ratio was restored to wild type, when discs of transgenic tubers were incubated at 21% (v/v) oxygen. (f) Starch decreased from the periphery to the center of the tuber. This decrease was much steeper in the transgenic lines, leading to lower starch content especially near the center of the tuber. (g) Metabolic fluxes (based on redistribution of (14)C-glucose) and ATP to ADP ratios were analyzed in more detail, comparing discs incubated at various external oxygen tensions (0%, 1%, 4%, 8%, 12%, and 21% [v/v]) with intact tubers. Discs of Suc phosphorylase-expressing lines had similar ATP to ADP ratios and made starch as fast as wild type in high oxygen but had lower ATP to ADP ratios and lower rates of starch synthesis than wild type at low-oxygen tensions typical to those found inside an intact tuber. (h) In discs of wild-type tubers, subambient oxygen concentrations led to a selective increase in the mRNA levels of specific SuSy genes, whereas the mRNA levels of genes encoding vacuolar and apoplastic invertases decreased. (i) These results imply that repression of invertase and mobilization of Suc via the energetically less costly route provided by SuSy is important in growing tubers because it conserves oxygen and allows higher internal oxygen tensions to be maintained than would otherwise be possible.
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PMID:A bypass of sucrose synthase leads to low internal oxygen and impaired metabolic performance in growing potato tubers. 1291 61