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Metabolism and Enzymology

D-Glucosone and L-Sorbosone, Putative Intermediates of L-Ascorbic Acid Biosynthesis in Detached Bean and Spinach Leaves ¹

Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164-6340

D-[6-¹⁴C]Glucosone that had been prepared enzymically from D-[6-¹⁴C]glucose was used to compare relative efficiencies of these two sugars for L-ascorbic acid (AA) biosynthesis in detached bean (Phaseolus vulgaris L., cv California small white) apices and 4-week-old spinach (Spinacia oleracea L., cv Giant Noble) leaves. At tracer concentration, ¹⁴C from glucosone was utilized by spinach leaves for AA biosynthesis much more effectively than glucose. Carbon-14 from [6-¹⁴C]glucose underwent considerable redistribution during AA formation, whereas ¹⁴C from [6-¹⁴C]glucosone remained almost totally in carbon 6 of AA. In other experiments with spinach leaves, L-[U-¹⁴C]sorbosone was found to be equivalent to [6-¹⁴C]glucose as a source of ¹⁴C for AA. In the presence of 0.1% D-glucosone, conversion of [6-¹⁴C] glucose into labeled AA was greatly repressed. In a comparable experiment with L-sorbosone replacing D-glucosone, the effect was much less. The experiments described here give substance to the proposal that D-glucosone and L-sorbosone are putative intermediates in the conversion of D-glucose to AA in higher plants.

¹ Supported by a grant from Hoffmann-LaRoche Inc. and Project 0266, College of Agriculture and Home Economics Research Center, Washington State University, Pullman, WA 99164.

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