Glucose acceptors

Arsenate, which can apparently serve as glucose acceptor to the enzyme-D-glucose complex but which does not form a stable glucose ester, causes the rapid decomposition of both sucrose and D-glucose-l-phosphate in accordance with the following equations 44... 

As glucose acceptor, however, such different substances as inorganic phosphate, keto-monosaccharides and an aldopentose can be used in... 

One might be tempted to bring some structural features of the phosphate ion in line with those of the glucose acceptors represented in XVI and XVIII. Thus, in the tetrahedral ion... 

Fig. 1. 1,6-Glycosylation with a glucose acceptor attached to a polymer support (P = solid support) and a trichloroacetimidate donor.

As a first attempt, the synthesis of sucrose was tried using the fully benzylat-ed donor 65 a and the commercially available crystalline 2,3,4,6-tetra-O-benzyl-a-D-glucopyranose as acceptor. The conditions were optimised to give as much fructofuranoside as possible and at the same time not to cause anomerisation of the glucose acceptor. As found earher with this approach, it was not possible to obtain a really good a/)S-ratio for the furanosidic linkage. Only a 20% yield of perbenzylated sucrose was achieved, the main product (50%) being the a,a-isomer [104]. 

Pless, D.D. Lennarz, W.J. (1977) Enzymatic Conversion of Proteins to Glycoproteins , Proceedings of the National Academy of Sciences, USA, 74,134-8 Pollack, L. Atkinson, P.H. (1983) Correlation of Glycosylation with Position in Amino-acid Sequence , Journal of Cell Biology, 97, 293-300 Pont-Lezica, R., Brett, C.T., Romero Martinez, P. Dankert, M.A. (1975) Glucose acceptor in plants with the properties of an a-saturated polyprenyl monophosphate . Biochemical and Biophysical Research Communications, 66, 980-7 Pont-Lezica, R., Romero, P. Dankert, M.A. (1976) Membrane-bound UDP-glucose. 

In this reaction, as well as in the phosphorolysis reaction, the enzyme acts as a n-glucose acceptor and is able to catalyze the exchange of an ester bond for a glycosidic bond. 

The mode of action of sucrose phosphorylase explains the observed role of arsenate in causing the hydrolytic decomposition of both sucrose and a-D-glucose 1-phosphate in the presence of the enzyme (195). Arsenate presumably acts as a D-glucose acceptor with the enzyme, to form an unstable D-glucose 1-arsenate compound, which hydrolyzes spontaneously to D-glucose and arsenate ... 

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