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  • Galactomannan  (2)
  • Endosperm  (1)
  • 1995-1999  (1)
  • 1980-1984  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Enzyme specificity in galactomannan biosynthesis (1995)
    Springer
    Planta 195 (1995), S. 489-495 
    Details
    ISSN: 1432-2048
    Keywords: Biosynthesis (computer simulation) ; Cell wall (plant) ; Cyamopsis ; Galactomannan ; Senna ; Trigonella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Membrane-bound enzymes from developing legume-seed endosperms catalyse galactomannan biosynthesis in vitro from GDP-mannose and UDP-galactose. A mannosyltransferase [mannan synthase] catalyses the extension of the linear (1→4)-β-linked d-mannan backbone towards the non-reducing end. A specific α-galactosyltransferase brings about the galactosyl-substitution of the backbone by catalysing the transfer of a (1→6)-α-d-galactosyl residue to an acceptor mannosyl residue at or close to the non-reducing terminus of the growing backbone. Labelled galactomannans with a range of mannose/galactose (Man/Gal) ratios were formed in vitro from GDP-[14C]mannose and UDP-[14C]galactose using membrane-bound enzyme preparations from fenugreek (Trigonella foenum-graecum L.), guar (Cyamopsis tetragonoloba (L.) Taub.) and senna (Senna occidentalis (L.) Link.), species which in vivo, form galactomannans with Man/Gal ratios of 1.1, 1.6 and 3.3 respectively. The labelled galactomannans were fragmented using a structure-sensitive endo-(1→4)-β-d-mannanase and the quantitative fragmentation data were processed using a computer algorithm which simulated the above model for galactomannan biosynthesis on the basis of a second-order Markov chain process, and also the subsequent action of the endo-mannanase. For each galactomannan data-set processed, the algorithm generated a set of four conditional probabilities required by the Markov model. The need for a second-order Markov chain description indicated that the galactomannan subsite recognition sequence of the galactosyltransferase must encompass at least three backbone mannose residues, i.e. the site of substitution and the two preceding ones towards the reducing end of the growing galactomannan chain. Data-sets from the three plant species generated three distinctly different sets of probabilities, and hence galactose-substitution rules. For each species, the maximum degree of galactose-substitution consistent with these rules was closely similar to that observed for the primary product of galactomannan biosynthesis in vivo. The data provide insight into the mechanism of action and the spatial organisation of membrane-bound polysaccharide synthases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195705
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Galactomannan formation and guanosine 5′-diphosphate-mannose: galactomannan mannosyltransferase in developing seeds of fenugreek (Trigonella foenum-graecum L., leguminosae) (1982)
    Springer
    Planta 155 (1982), S. 105-111 
    Details
    ISSN: 1432-2048
    Keywords: Galactomannan ; Endosperm ; Polysaccharide (biosynthesis, storage) ; Mannosyltransferase ; Seed (development) ; Trigonella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The time-course of galactomannan and stachyose (digalactosyl-sucrose) deposition in the fenugreek seed endosperm has been determined, and correlated with standard parameters of seed development. During, and only during, the period of galactomannan deposition, endosperm homogenates are capable of catalysing the transfer of labelled d-mannosyl residues from guanosine 5′-diphosphate d-[U-14C]mannose to a soluble polysaccharide product indistinguishable from galactomannan. The mannosyltransferase activity peaks twice, once at the beginning of galactomannan deposition, and again in the middle of the most rapid phase of galactomannan deposition. The enzyme in the later peak sediments with grossly particulate material (1,000 g pellet), whereas the earlier peak contains a considerable proportion of a particulate enzyme sedimenting at 100,000 g. These observations are discussed in the light of existing information on the ultrastructural aspects of galactomannan deposition. The mannosyltransferase is clearly involved in galactomannan formation in vivo, but the status of an accompanying galactosyltransferase is less clear.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392539
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    Paper (German National Licenses)
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