Sugar transfer

Durr C, Hoffmeister D, Wohlert SE et al (2004) The glycosyltransferase UrdGT2 catalyzes both C- and O-glycosidic sugar transfers. Angew Chem Int Ed 43 2962-2965... 

In Japan, the largest market for the S. rebaudiana sweeteners to date, three different forms of stevia sweetener products are commercially available, namely, stevia extract , sugar-transferred stevia extract , and rebaudioside A-enriched stevia extract . Stevia extract is a powder or granule made by several industrial steps and standardized so as to contain more than 80% of steviol glycosides, inclusive of dulcoside A (3-5%), rebaudioside A (20-25%), rebaudioside C (5-10%), and stevioside (50-55%) [31]. Sugar-transferred stevia extract is made by... 

Each enzyme is specific for the sugar transferred, its nucleotide precursor, the residue to which it is transferred and the bond formed. All are effectively irreversible transfers and all the enzymes are membrane-bound. The rhamnosyl and mannosyl transferases can be solubilised with non-ionic... 

The symbols in Table 4.3 refer to the final amounts of each sugar transferred, but the rates of transfer were also analysed. The addition of a second sialyl residue to acceptor B, catalysed by enzyme 2 was slow, even though a final addition of 80 per cent of the theoretical saturation value was achieved. Similarly, the addition of a sialyl residue to acceptor D, catalysed by enzyme 1 was very slow (and incomplete). Consequently, neither of these reactions would contribute greatly to the pattern of overall synthesis except under... 

Monophosphate Glucose The Product Formed with Endogeneous Microsomal Acceptor Proceedings of the National Academy of Sciences, U.S.A., 68, 2857-60 Behrens, N.H., Parodi, A.J., Leloir, L.F. Krisman, C.R. (1971) The Role of Dolichol Monophosphate in Sugar Transfer , Archives of Biochemistry and Biophysics, 143,... 

The truncated, soluble recombinant enzymes contain two distinct sugar transfer domains. If the aspartates (D) are mutated in one domain, then that glycosyltransferase activity is destroyed, but the other domain functions normally. The PmHSl and 2 domain structures are still being delineated... 

The native Pasteurella and the recombinant Escherichia co//-derived preparations of the various microbial Pasteurella GAG synthases rapidly form long polymer chains in vitro (2). The sugar transfer specificity of the native-sequence enzymes is exquisite and only the authentic sugars are incorporated into polymer products. For example, the native synthase enzymes do not utilize significantly the C4 epimer precursors in comparison to the natural UDP-sugars. 

However, as described later, the sugar acceptor specificity is not as precise as the sugar transfer specificity allowing one synthase to extend non-cognate GAG polymers to create chimeric polysaccharides. 

Figure 7. Analysis of various chimeric synthases. Portions of the pmHAS (black) and pmCS (white) enzymes were fused to produce chimeric enzymes. The constructs were tested for sugar transfer activity (HAS, HA synthase CS, chondroitin synthase GlcUA transferase) in vitro. The last enzyme, pmCHC, had relaxed specificity and could incorporate either UDP-hexosamine.

The substance involved in sugar transfer reactions in bacteria is undecaprenol which has n=ll and 2 trans double bonds. A similar compound ficaprenol is present in plants. It has n=ll and 3 trans double bonds. It was isolated as the free alcohol after treatment of leaves with strong alkali and at present there is no evidence that its derivatives act as intermediates in sugar transfer. 

The mechanism of direct participation of retinoids in the transfer of mannose to glycoconjugates is appealing in light of the broad implications of changes in cell surface glyconjugates in control of cell growth, differentiation, and transformation (see Section VI). However, firm conclusive evidence must still be provided to demonstrate a role for retinoids distinct from that of dolichol. Furthermore, a satisfactory metabolic scheme for the direct participation of retinoic acid and its derivatives in sugar transfer reactions does not yet exist. Future experiments must be addressed to these two important questions. 

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