D-glucosone and L-sorbosone as putative intermediates in the biosynthesis of L-ascorbic acid in plants

Conference · Wed Apr 01 04:00:00 EST 1987 · Plant Physiol., Suppl.; (United States)

OSTI ID:6077341

Loewus, M W; Nick, J A; Bedgar, D L; Loewus, F A

In plants, biosynthesis of L-ascorbic acid (AA) from D-glucose (glc) proceeds without carbon chain inversion. This requires oxidation of C1 and C2, and epimerization at C5. Neither sequence of reactions nor enzymes involved is yet known. To examine the overall reaction the authors fed D-(6-/sup 14/C)glucosone to bean seedlings. It was converted to AA as effectively as (6-/sup 14/C)glc with virtually no redistribution of label into the opposite terminal carbon. In other studies, a NADP-dependent L-sorbosone dehydrogenase that synthesized AA was isolated from bean and spinach leaves. Partial purification by precipitation at 45-55% (NH/sub 4/)/sub 2/SO/sub 4/, fractionation on DEAE cellulose, and molecular sieving on Sephadex G-200 gave 30-fold purification. The enzyme was stable at -20/sup 0/C for several months. The apparent Km for sorbosone (0.9 mM NADP/sup +/) was 11.3+/-1.9 mM and for NADP/sup +/ (50 mM sorbosone) was 145+/-47 ..mu..M. The relatively high Km's may reflect a two-step process or selection of a minor isomeric forms or sorbosone. A pathway (possibly involving phosphorylated intermediates) is suggested: D-Glucose..-->..D-Glucosone..-->..L-Sorbosone..-->..L-Ascorbic acid.

• Research Organization: Washington State Univ., Pullman
• OSTI ID: 6077341
• Report Number(s): CONF-8707108-
• Conference Information: Journal Name: Plant Physiol., Suppl.; (United States) Journal Volume: 83:4
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ADSORBENTS
ASCORBIC ACID
BEANS
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL PATHWAYS
BIOSYNTHESIS
CARBON 14 COMPOUNDS
ENZYMES
FOOD
FRACTIONATION
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
MOLECULAR SIEVES
NUCLEOTIDE DEHYDROGENASES
OXIDOREDUCTASES
PLANTS
PRECIPITATION
PURIFICATION
REACTION KINETICS
SEEDLINGS
SEPARATION PROCESSES
SPINACH
STEREOCHEMISTRY
SYNTHESIS
TRACER TECHNIQUES
VEGETABLES
VITAMINS