Utilization of D-Glucuronate by Corn Coleoptiles.

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Abstract
Out of a variety of tissues tested, young corn coleoptile was superior in its ability to decarboxylate D-glucuronic acid-C14 under aerobic conditions. By comparing radio-chemical yields in the d14Oo produced from D-glucuronic acid-6-C14 and D-glucuronic acid-U-C14 by 1-g coleoptiles, it was shown that, over a period of about 12 hours (during which nearly half of the 20 micromoles of substrate supplied had been utilized) the only carbon from the substrate to appear in the CO2 was that from C-6. D-Glucuronolactone-Cl4 was also decarboxylated, and the slices were shown to bring about the hydrolysis of the lactone to the free acid. No soluble products of the decarboxylation of D-glucuronic acid-U-Cl4 could be detected, but the insoluble residue after 80% alcohol extraction or 10% trichloroacetic acid precipitation contained 5 times as much radioactivity as the respired CO2. Hydrolysis of this material revealed that the bulk of the radioactivity was in D-xylose units derived from polysaccharide. This suggests that xylan synthesis and decarboxylation of D-glucuronate are very closely linked. Other evidence on the origin of D-glucuronate and its utilization is also summarized, and the present experiments lend support to some recent proposals of Altermatt and Neish implicating UDP-glucose, UDP-glucuronate and UDP-xylose in xylan synthesis from glucose in plant tissues.