Metabolism of galactosylononitol in seeds of Vigna umbellata

In this paper, we describe the occurrence of a new galactosylononitol synthase activity (GOS) in seeds of Vigna umbellata. The enzyme catalyzed the reversible galactosyl transfer from galactinol to D-ononitol (1D-4-O-methyl-myo-inositol), yielding galactosylononitol (O-alpha-D0galactopyranosyl-(1 to...

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Bibliographic Details
Published in:Plant and cell physiology 1998-03, Vol.39 (3), p.334-341
Main Authors: Peterbauer, T. (University of Vienna (Austria)), Puschenreiter, M, Richter, A
Format: Article
Language:English
Subjects:
Agronomy. Soil science and plant productions
AZUCARES ALCOHOLES
Biological and medical sciences
BIOSINTESIS
BIOSYNTHESE
BIOSYNTHESIS
Cyclitols
Economic plant physiology
Enzymes
ESTAQUIOSA
Fundamental and applied biological sciences. Psychology
GALACTOSA
GALACTOSE
Galactosylononitol synthase
GRAINE
METABOLISM
METABOLISME
METABOLISMO
Nutrition. Photosynthesis. Respiration. Metabolism
Plant physiology and development
SEEDS
SEMILLA
STACHYOSE
Stachyose synthase
SUCRE ALCOOL
SUGAR ALCOHOLS
VIGNA UMBELLATA
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Summary:In this paper, we describe the occurrence of a new galactosylononitol synthase activity (GOS) in seeds of Vigna umbellata. The enzyme catalyzed the reversible galactosyl transfer from galactinol to D-ononitol (1D-4-O-methyl-myo-inositol), yielding galactosylononitol (O-alpha-D0galactopyranosyl-(1 to 3)-4-O-methyl-D-myo-inositol) and myo-inositol. A brief characterization of the enzyme indicated a native molecular mass of 96 kDa and K(m) values for galactinol and ononitol of 3.7 mM and 10.2 mM, respectively. The GOS activity could not be separated from stachyose synthase (STS) by anion-exchange and size-exclusion chromatography, suggesting that the two reactions are catalyzed by very similar enzymes or by the same enzyme. An equilibrium constant of 0.8 was determined for galactosyl ononitol synthesis. Thus, the group transfer potential of galactosylononitol is similar to that of galactinol and sufficient for galactosylation of raffinose family oligosaccharides. It was demonstrated that galactosylononitol can substitute for galactinol in the STS catalyzed synthesis of stachyose. Galactosylononitol and GOS activity were initially detected halfway through seed development. In mature seeds stachyose was the predominant sugar, followed by sucrose and galactosylononitol. A metabolic pathway for galactosylononitol in the seeds of V. umbellata is proposed
ISSN:0032-0781
1471-9053
DOI:10.1093/oxfordjournals.pcp.a029374