Acceptor-bound carbohydrate

In one scenario, the first carbohydrate is anchored via its reducing end (see Scheme 2.1, case 1). Here the support-bound carbohydrate will function as an acceptor in the coupling step to a solution-based donor D. As the next cycle is contemplated, a unique acceptor hydroxyl must be exposed in the now elongated, resin-bound carbohydrate constmct. 

Fig. 3. Acceptor-bound solid-phase carbohydrate synthesis.

Our approach to oligosaccharide synthesis relied on the acceptor-bound solid-phase method. This method formally reduces the synthesis of carbohydrates to a repetitive cycle of glycosylation and deprotection events. It was reasoned that the repetitive nature of an acceptor-bound glycosylation method rendered it ideal for automation. Therefore, we set out to investigate the potential variables in such a scheme. 

Our laboratory decided to utilize an acceptor-bound approach for the carbohydrate assembly, whereby the anomeric position of the first carbohydrate is attached at its reducing end to the solid support [9, 10], Therefore, glycosyl... 

The ability of water to act as both donor and acceptor of hydrogen bonds makes it an excellent mediator in protein-carbohydrate complexes. Results of numerous X-ray crystallographic studies of protein-carbohydrate complexes attest to the pervasiveness of water-mediated hydrogen bonds in protein-carbohydrate interactions. Lectin-bound water molecules are proposed to act as an extension of the protein surface itself [1]. This idea is supported by the fact that water molecules occupy conserved sites in the structures of related lectins [24]. In addition, water molecules can mediate similar hydrogen bonding interactions in the complexes of different proteins with a specific carbohydrate ligand or in complexes of the same lectin with different saccharide ligands [1]. 

Essentially similar results have been obtained by Eylar and co-workers " on the biosynthesis of bovine submaxillary mucin. The enzyme is firmly bound to a membrane solubilization by Triton X-100 results in a large increase in enzymic activity." The enzyme was purified by gel filtration, and its properties were studied. Among various substances studied, the only one (besides carbohydrate-free mucins) that was active as the acceptor of 2-acetamido-2-deoxy-D-galactose was a basic protein, called encephalitogen, isolated from bovine, spinal-cord myelin. ... 

Transaldolation a reaction of carbohydrate metabolism, in which a C3-unit (equivalent to a dihy-droxyacetone unit) is transferred from a ketose to an aldose. T. is catalysed by transaldolase (EC 2.2.1.2). The C3-unit does not exist in the free state, but remains bound to the e-group of a lysine residue in the enzyme (Fig ). Only fructose 6-phosphate and sedoheptulose 7-phosphate are cleaved by transaldolase. Acceptors for the C3-unit are the aldose phosphates, o-glyceraldehyde 3-phosphate, D-erythrose 4-phosphate and more rarely ribose 5-phosphate. There is no coenzyme and the mechanism of reaction is similar to that of aldolase (EC 4.1.2.13). 

CO2 must be reduced to carbohydrate by means of the hydrogen set free by photolysis. This reduction takes place only after the CO2 has been bound to an organic acceptor. The binding and the reduction of the CO2 are known as the secondary processes of photosynthesis. 

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