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Metabolism and Enzymology

Conversion of L-Sorbosone to L-Ascorbic Acid by a NADP-Dependent Dehydrogenase in Bean and Spinach Leaf ¹

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

An NADP-dependent dehydrogenase catalyzing the conversion of L-sorbosone to L-ascorbic acid has been isolated from Phaseolus vulgaris L. and Spinacia oleracea L. and partially purified. It is stable at –20°C for up to 8 months. Molecular masses, as determined by gel filtration, were 21 and 29 kilodaltons for bean and spinach enzymes, respectively. K_m for sorbosone were 12 ± 2 and 18 ± 2 millimolar and for NADP⁺, 0.14 ± 0.05 and 1.2 ± 0.5 millimolar, for bean and spinach, respectively. Lycorine, a purported inhibitor of L-ascorbic acid biosynthesis, had no effect on the reaction.

¹ This work was supported by Hoffmann-La Roche Inc., Nutley, NJ, and grant DE-FG06-88ER 13890, Office of Energy Research, U.S. Department of Energy. A scientific paper from the College of Agriculture and Home Economics Research Center, Washington State University, Pullman, WA 99164.

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