This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: verbascose biosynthesis I (galactinol-dependent)
|Superclasses:||Biosynthesis → Carbohydrates Biosynthesis → Oligosaccharides Biosynthesis|
Some taxa known to possess this pathway include : Pisum sativum
Expected Taxonomic Range: Fabaceae
Verbascose and ajugose are two members of the so-called 'raffinose series' of sucrosyl oligosaccharides (also known as raffinose family oligosaccharides, RFOs). Sucrosyl oligosaccharides represent a large portion of primary oligosaccharides in plants (defined as oligosaccharides synthesized by the action of a glycosyl transferase that mediates the transfer of a glycopyranosyl residue to either the glucopyranosyl or fructofuranosyl moiety of sucrose. They are differentiated from secondary oligosaccharides which are generated by the hydrolysis of higher oligosaccharides, polysaccharides or heterosides. For review, see [Kandler82]). Members of the raffinose series occur at least in traces in each plant family; it is one of the most widespread sucrosyl oligosaccharide series in flowering plants and might even be ubiquitous (see [Kandler82] for review). This series comprises raffinose, stachyose, verbascose, ajugose as well as several other compounds with a higher degree of polymerization (DP; the highest is a nonasaccharide; none of these higher-DP oligosaccharides in the series have not yet been named). The sugars of this series consist of α1,6-linked chains of D-galactose attached to the 6-glucosyl position of sucrose. They are synthesized in leaves, roots and tubers. Raffinose and stachyose are the two most commonly found oligosaccharides of this series (see stachyose biosynthesis). However, higher RFOs with DP are also found in certain species such as the frost-hardy Ajuga reptans, in which both short-chain and long-chain RFOs are present and have been speculated to act as antifreeze or antisalt agents [Bachmann94, Bachmann95, Gilbert97, Sprenger00]. The biosynthesis of higher-DP RFOs appears to occurs via two routes: one is dependent on galactinol, and requires enzymes similar to that of the stachyose biosynthesis pathway (this pathway), the other does not appear to require galactinol (see ajugose biosynthesis II (galactinol-independent)).
Enzymes of the pathway: A single enzyme has been described that can catalyze both polymerization steps of this pathway. This enzyme, galactinol:raffinose galactosyltransferase, catalyzes the chain elongation of RFOs by transferring the α-galactosyl residue of galactinol to RFO molecules. The enzyme appears to be primarily a stachyose synthase catalyzing the galactosylation of raffinose into stachyose. However, it was shown to also use stachyose and verbascose as substrates.
Bachmann94: Bachmann M, Matile P, Keller F (1994). "Metabolism of the Raffinose Family Oligosaccharides in Leaves of Ajuga reptans L. (Cold Acclimation, Translocation, and Sink to Source Transition: Discovery of Chain Elongation Enzyme)." Plant Physiol 105(4);1335-1345. PMID: 12232288
Bachmann95: Bachmann M, Keller F (1995). "Metabolism of the Raffinose Family Oligosaccharides in Leaves of Ajuga reptans L. (Inter- and Intracellular Compartmentation)." Plant Physiol 109(3);991-998. PMID: 12228647
Kandler82: Kandler O., Hopf H. (1982). "Oligosaccharides based on sucrose (sucrosyl oligosaccharides)." In Plant Carbohydrates I- Intracellular carbohydrates, Encyclopedia of plant physiology New Series Vol 13A, Springer-Verlag eds. Chapter 8. pp. 348.
Peterbauer02: Peterbauer T, Mucha J, Mach L, Richter A (2002). "Chain Elongation of raffinose in pea seeds. Isolation, characterization, and molecular cloning of mutifunctional enzyme catalyzing the synthesis of stachyose and verbascose." J Biol Chem 277(1);194-200. PMID: 11675396
Peterbauer02a: Peterbauer T, Mach L, Mucha J, Richter A (2002). "Functional expression of a cDNA encoding pea (Pisum sativum L.) raffinose synthase, partial purification of the enzyme from maturing seeds, and steady-state kinetic analysis of raffinose synthesis." Planta 215(5);839-46. PMID: 12244450
Peterbauer03: Peterbauer, T., Karner, U., Mucha, J., Jones, D.A., Hedley, C.L., Richter, A. (2003). "Enzymatic control of the accumulation of verbascose in pea seeds." Plant, Cell and Environment, 26:1385-1391.
Sprenger00: Sprenger N, Keller F (2000). "Allocation of raffinose family oligosaccharides to transport and storage pools in Ajuga reptans: the roles of two distinct galactinol synthases." Plant J 21(3);249-58. PMID: 10758476
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