In glycosyl transfer reactions

The first evidence showing that plant polyprenols involved in glycosyl-transfer reactions are not allylic, but a-saturated, like animal dolichol (2), came from Pont Lezica and coworkers.23 The authors postulated that the presence of sugar acceptors having the properties of a-saturated polyprenyl phosphates may be a general feature of eukaryotic cells, in contrast to the a-unsaturated polyprenyl phosphates characteristic of prokaryotic cells. 

Further work in plant systems confirmed, by different methods (biosynthesis from mevalonate,27 28 mass spectrometry,33 and the techniques already mentioned30), that the polyprenyl phosphate involved in glycosyl-transfer reactions is dolichyl phosphate. Table II shows different sources from which dolichyl phosphate has been identified in plants. 

DeLuca H (1977) The direct involvement of vitamin A in glycosyl transfer reactions of mammalian membranes. Vitamins and Hormones 35,1-57. 

Pigman, eds). Academic Press, New York, pp. 256-84 De Luca, S. (1977a) Incorporation of Mannose and Glucose into Prenylphosphate Sugars in Isolated Human Platelet Membranes , Biochimica et Biophysica Acta, 498, 341-8 De Luca, L.M. (1977b) The Direct Involvement of Vitamin A in Glycosyl Transfer Reactions of Mammalian Membranes , Vitamins and Hormones, 35,1-57 De Luca, L.M. (1978) Vitamin A , in Handbook of Lipid Research (H.F. De Luca, ed.),... 

Dolichoprenols (Cgo to C105) are derived from Z elongation of , -famesyl pyrophosphate and are universal components of eukaryotic cells. These compounds function in glycosyl transfer reactions (Waechter and Lennarz, 1976). 

Dolichol is related to vitamin A (10.66a), the phosphate ester of which may also be involved in glycosyl transfer reactions in the body (Chapter 11). Polyprenol pyrophosphates are involved in the biosynthesis of rubber, gutta-percha and other terpenes (Chapter 11.5). 

A. Cofactor Role of Retinoids in Glycosyl Transfer Reactions... 264... 

Apart fi-om effects on the nucleus, retinol has been found to have a stabilizing effect on cell membranes. More specifically retinol seems to take part in glycosyl-transfer reactions and the synthesis of various glycoconjugates (page 407). Effects on cell surface components may mediate changes in intracellular recognition and interactions and also in the process of cell adhesion and aggregation. 

The lack of glycosyl transfer reaction is the class of pectinolytic hydrolases is in agreement with the observed inversion of the anomeric configuration of the newly formed reducing ends of the products. All three polygalacturonases studied here utilize the single displacement mechanism of hydrolysis. 

There is one common feature of all transfer studies. If a substance can function as an acceptor, it must evidently have a higher affinity for the enzyme than has water, because, in all these reactions, water (used as the solvent) is present in large excess. This holds for other glycosyl transfer reactions as well. 

In the next step, a 2-acetamido-2-deoxy-D-glucosyl group is transferred from its UDP derivative onto the monosaccharide-lipid intermediate, to form the disaccharide-lipid intermediate (see Reaction II of Scheme 3). This is a glycosyl-transfer reaction of the more usual type, and UDP is released as a product of the reaction. ... 

Seibel et al. [36] reported, for the first time, the use of microwave heating in the glycosylation of amino acids. They performed glycosyl transfer reactions of perace-tylated monosaccharides (glucose and galactose) and disaccharides (maltose and lactose) with N-9-fluorenylmethoxycarbonyl-L-serine benzyl ester in the presence of iron trichloride with short reaction times (4 min, compared with 5-10 h by conventional heating) and with improved yields (52-61% compared with 10-31% by conventional heating). It is worthy of note that in these reactions heavy metal compounds, for example silver trifluoromethanesulfonate, mercury dibromide and di-cyanide, or boron trifluoride-diethyl etherate, can be replaced by the environmentally safe promoter iron trichloride. 

Glycosylation transfer reaction catalyzed by GGTase is divided into four types hydrolysis reaction, cychzation reaction, couphng reaction and disproportionation reaction, in which the coupling reaction in some documents is also known as the open-loop reaction. The direction of glycosylation reaction catalyzed by the GGTase depends on the reaction rate constant of the four types of reaction. Typically, the rate constant of cychzation reaction is greater than that of the hydrolysis reaction, and therefore the direction of the reaction is mainly to produce GD (Fig. 2.3). 

In the detailed description of glycosyl transfer reactions and polymer... 

Replacement of the asparaginyl group by aspartyl or glutaminyl residues led to a total loss of acceptor activity, as did the replacement of the threonyl residue by valine. This accords with the idea that the sequence Asn-X-Thr/ Ser is essential for transfer. The exchange of the leucyl group for lysine or glycine did not impair acceptor function in any way, but the insertion of an aspartyl residue reduced the effectiveness of the peptide in the transfer reaction by 7 5 per cent. If proline replaced leucine, the peptide would not function at all in the glycosyl transfer. 

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