The project aim was to determine which of the competing pathways predominate(s) <i>in vivo</i> in the formation of the UDP-GlcA, GDP-GalA and UDP-Man utilised for plant cell wall synthesis. The studies conducted on the <sup>3</sup>H:<sup>14</sup>C ratios of plant cell wall residues at 8 h indicate that UDP-Gal is not a significant direct precursor of UDP-GalA. The <sup>3</sup>H:<sup>14</sup>C ratios of the intermediary metabolites were studied over time. The results show that the <sup>3</sup>H:<sup>14</sup>C ratio kinetics of UDP-GalA and UDP-Gal are vastly different from one another. These results also indicate that UDP-Gal is not a significant direct precursor of UDP-GalA. The <sup>3</sup>H:<sup>14</sup>C ratios of the AIR (alcohol insoluble residue)-derived monosaccharides indicate that UDP-GlcA, UDP-GalA, UDP-Xyl, UDP-Ara and UDP-Api, like UDP-Rha, arose mainly from the UDP-Glc ‘core’ metabolite. The <sup>3</sup>H:<sup>14</sup>C ratio kinetics of UDP-GalA, UDP-GlcA, UDP-Xyl and UDP-Ara are very distinct from the <sup>3</sup>H:<sup>14</sup>C ratio kinetics of Glc 6-P but they are similar to the isotope ratio kinetics of UDP-Glc. The <sup>3</sup>H:<sup>14</sup>C ratios of the AIR-derived monosaccharides and <sup>3</sup>H:<sup>14</sup>C ratios of the intermediary metabolites give strong evidence that UDP-GalA and UDP-GlcA are predominantly formed by the UDP-Glc dehydrogenase pathway and not the <i>myo-</i>inositol pathway. The <sup>3</sup>H:<sup>14</sup>C ratios kinetics of UDP-Glc are approximately equal to those of Glc 1-P. It is observed that the <sup>3</sup>H:<sup>14</sup>C ratio of AIR-derived GalA residue is greater than for Man and Fuc. As UDP-GalA was determined to arise predominantly from UDP-Glc, GDP-Man and GDP-Fuc cannot also stem from Glc 1-P. The predominant pathway of GDP-Man synthesis must be via Gla 6-P or Fru 6-P. The <sup>3</sup>H:<sup>14</sup>C ratio of Rib was similar to those of GalA, Ara, Xyl and Api. A pathway is known to exist that may convert to UDP-Xyl to the RNA precursor Rib 5-P. The results suggest that this is the predominant pathway of Rib synthesis for RNA.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:661811 |
| Date | January 2005 |
| Creators | Sharples, Sandra Christina |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12919 |
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