Apiose metabolism

Isomers of D-apiofuranosyl 1-phosphate have been prepared by treating a mixture of jS-o-apio-D-furanosyl and /3-D-apio-L-furanosyl tetra-acetates with crystalline phosphoric acid. a-o-Apio-o- (59) and a-o-apio-L-furanosyl-1-phosphate (60) and their cyclic phosphates were separated by chromatography and identified by H n.m.r. o-Apiose is metabolized in parsley and Lemna minor with the possible formation of UDP-D-apiose. L. minor will convert UDP-a-glucuronic acid into a-o-apio-D-furanosyl-1,2-cyclic phosphate (61) but no evidence of UDP-o-apiose was found, although it is possible that (61) arose from the rapid hydrolysis of UDP-o-apiose. 

The metabolism of apiose in plants has not been investigated extensively. It has been suggested80 that apiose could give rise to simple terpenes by condensation and reduction. Incubation of [ -,4C]apiose in parsley plants resulted in negligible, but unspecified, amounts of carbon-14 incorporated into apiin.66 The specific activity of the [ -14C]apiose administered was low (5 X 105 d.p.m./jumole) for this reason, the data suggested only that no highly active mechanism is available in parsley for the metabolism of this branched-chain sugar. 

Incubation of D-[U-I4C]apiose with sterile Lemma minor (duckweed) produced less than 0.01% incorporation into the cell-wall polysaccharides.75 Most of the d-[U-i4C]apiose appeared as 14C02 some remained in solution in the medium and in the duckweed plants, primarily as degradation products of D-[U-14C]apiose, but not as the branched-chain sugar.75 There is an efficient synthesis of the [U-14C]apiose moiety of cell-wall polysaccharides from D-[U-14C]glucose under similar conditions.81 Of the plant tissues tested, only L. minor contained an enzyme system able to metabolize free apiose. Carrot, lettuce, and spinach tissues are unable to metabolize the free, branched-chain sugar.75... 

Roberts, R.M., Shah, R., and Loewus, F., 1967b, Inositol metabolism in plants. IV Biosynthesis of apiose in Lemna and Petroselinum. Plant Physiol. 42 659-666. 

In some respects it is surprising that ring-opening and rearrangement is not a more common feature of sugar nucleotide metabolism and it seems likely that the system for producing the branched chain of apiose is an evolutionary derivative of the normal decarboxylase reaction. 

D-Apiose (31) is synthesized from D-glucuronic acid metabolism in a reaction that involves loss of the carboxyl group and C-3 of D-glucuronic acid. The enzyme which requires NAD" has been isolated (Grisebach, 1980). 

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