Fructans synthesis

Koops, AJ. and Jonker, H.H., Purification and characterization of the enzymes of fructan biosynthesis in tubers of Helianthus tuberosus Columbia. 1. Purification of sucrose sucrose 1-fructosyltransferase and reconstruction of fructan synthesis in vitro with purified sucrose sucrose 1-fructosyl transferase and fructamfructan 1-fructosyltransferase, Plant Physiol., 110, 1167-1175, 1996. 

Tuber structure in cross section from exterior to interior can be separated into the epidermis, cortex, outer medulla, inner medulla, and pith (Mazza, 1985). Relatively little is known about the temporal sequence of cell division and differentiation leading up to bulking. Sink capacity is a function of the combined vacuolar volume of the tubers, the location of fructan synthesis and storage within the cells (Darwen and John, 1989 Keller et al., 1988 Pollock, 1986). Vacuolar volume is a function of cell size and number. The size of individual cells within the tuber varies with tissue type cortex (286 cells per 10 mm2), extension zone (145 cells per 10 mm2), storage tissue (85 cells per 10 mm2), and pith (149 cells per 10 mm2) (Schubert and Feuerle, 1997). The extent that cell number and size increases after the initial formation of the tuber has not been adequately documented. 

Dickerson, 1966 Wiemken et al., 1986). Therefore, low sucrose content is essential during fructan synthesis otherwise, 1-FFT merely transfers the fructosyl unit from 1-kestose to sucrose, forming the same products as the reactants (i.e., 1-kestose and sucrose). Both enzymes (1-SST and 1-FFT) are localized in the vacuole (Carpita et al., 1991 Darwen and John, 1989 Frehner et al., 1984). 

Nagaraj, V.J., Altenbach, D., Galati, V., Luscher, M., Meyer, A.D., Boiler, T., and Wiemken, A., Distinct regulation of sucrose sucrose-l-fructosyltransferase (1-SST) and sucrose fructan-6-fructosyltrans-ferase (6-SFT), the key enzymes of fructan synthesis in barley leaves 1-SST as the pacemaker, New Phytol., 161, 735-748, 2004. 

A fructan-produclng bacterium was Isolated from soils and characterized for polysaccharide synthesis. The composition and properties of the polysaccharide produced were studied. The organism. Identified as a strain of Bacillus polvmvxa. produced a large quantity of polysaccharide when grown on sucrose. 

Inulin biosynthesis in Jerusalem artichoke occurs via the combined action of two enzymes l-sucrose sucrose fructosyltransferase (1-SST) and l-fructan fructan fructosyltransferase (1-FFT). 1-SST catalyzes the synthesis of inulins of a low degree of polymerization, while 1-FFT catalyzes the synthesis of ffuctans of a degree of polymerization up to 50 (Sevenier et al., 2002a). High... 

Noel, G.M. and Pontis, H.G., Involvement of sucrose synthase in sucrose synthesis during mobilization of fructans in dormant Jerusalem artichoke tubers, Plant Sci., 159, 191-195, 2000. 

Shiomi, N., Properties of fructosyltransferases involved in the synthesis of fructan in Liliaceous plants, J. Plant Physiol., 134, 151-155, 1989. 

Fructofuranose is found in probably the most well-known and commercially available of all carbohydrates, sucrose. Various derivatives of sucrose are also known in nature, e.g. fatty acid derivatives [91] and agrocinopines [92]. Fructo-furanosides are also present in various plant and bacteria polysaccharides, most often as fructans, but sometimes as a singular component in repeating units [2, 93]. Syntheses of sucrose or derivatives thereof are not very frequent [41, 94-96], and oligosaccharide synthesis with fructofuranosyl donors are even more scarce. 

This obvious structural difference between plant and bacterial inulin has its origin in the individual synthesis related system. Feedstock for both inulins is sucrose. However, the plant inulin production is a two-step reaction, starting with a sucrose-1-fructosyltransferase (1-SST). One sucrose molecule acts as donor and a second one as acceptor of a fructosyl unit. This leads to the formation of the trisaccharide 1-kestose. Catalyzed by a fructan-fructan-1-fructosyltransferase (1-FFT), fructosyl units are shuffled between the 1-kestose and higher polymeric p-(2 1) linked fructan molecules in the second step. Repetition of this step results in inulin with (3-(2 1) linkages only [129-132]. 

Only the fructosyltransferase (FTF, EC 2. 4. 1. 9) is required in bacteria for the synthesis of bacterial inulin. The enzyme shuffles fructosyl units from one sucrose molecule (acting as druior) to another sucrose molecule, 1-kestose, and higher polymeric p-(2 1) linked fructan molecules, respectively (acting as acceptor). This enzyme partly leads to p-(2—>6) linkages, which results in branches within the inulin molecule [130, 133]. 

Information on the metabolism of D-fructans is derived mainly from examination of inulin. Sucrose-sucrose 1-fructosyltransferase (SST) and transfructosylase (FFT) are responsible for the synthesis of D-fructans, whereas hydrolases A and B are involved in their breakdown. 

Sucrose is the sole source for synthesis of D-fructan in artichoke tubers.206 Thus, the level of this disaccharide can play an important role in the regulation of enzyme activities.202,203,207 Sucrose strongly inhibits the enzymic hydrolysis of inulin by D-fructan hydrolases, as... 

An entirely different ester is D-fructosyl phosphate, both ring forms of which, (14) and (15), were synthesized, isolated, and identified. Important as a possible intermediate in the biochemical synthesis and breakdown of the fructans, the pyridine salt of the 1-phosphate (12) was treated with dicyclohexylcarbodiimide, to form the cyclic 1,2-ester (13), which is very labile and is hydrolyzed to a mixture of both forms, (14) and (15), of the 2-phosphoric ester. This cycUzation mechanism was first mentioned by Khorana and coworkers, and later confirmed. Separation was effected... 

Bacillus subtilis levansucrase (sucrose 2,6-/8-D-fructan 6-)8-D-fructosyltrans-ferase, EC 2.4.1.10) catalyzes fructosyl transfer from sucrose to levan (154). In the absence of a fructosyl acceptor, the primary reaction is sucrose hydrolysis, although a limited amount of self-initiated levan synthesis occurs as well (155). As with sucrose phosphorylase, acceptor specificity is broad a number of saccharides and other nucleophiles are suitable fructosyl acceptors (154-158). The complete amino acid sequence of the approximately SO-kDa enzyme has been determined by both protein (159) and gene (160) sequence analyses. The three-dimensional structure at 3.8 A reveals a rod- or ellipsoid-shaped protein with a length some four times the diameter (161). 

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