Glycosyl group, enzymic transfer

Transferases. Enzymes which transfer a group, possibly a methyl group or a glycosyl group, from one compound to another. The name of the group transferred is usually in-... 

The chymotiypsin reaction is one example of acyl group transfer (see Fig. 6-21). Glycosyl group transfers involve nucleophilic substitution at C-l of a sugar ring, which is the central atom of an acetal. In principle, the substitution could proceed by an SnI or Sn2 path, as described for the enzyme lysozyme (see Fig. 6-25). 

D being a glycosyl group. The reaction occurs in two main steps, formation of a glycosyl enzyme, and transfer of the glycosyl group to a water molecule. 

The classic enzyme commission (EC) classification for GTs is on the basis of their donor and acceptor specihcity as well as the product formed. Currently, 295 entries are in this database (http //www.chem.qmul.ac.uk/iubmb/). The distinction between these enzymes is noted by their ability to catalyze the transfer of hexoses (EC 2.4.l.y, hexosyltransferases), pentoses (EC 2.4.2.y, pentosyltransferases), or other glycosyl groups (2.4.99.y, sialyltransferases). This classification is restricted to enzymes that are fully characterized, and it can be problematic for enzymes that act on several distinct acceptors but at different rates. It also does not take into account the origin of the enzyme or its three-dimensional stmcture. 

These enzymes transfer functional groups between donors and acceptors. The AMINO, ACYL, PHOSPHATE, ONE CARBON and GLYCOSYL are the major groups that are transferred, e. g. A— X+ B-k A+ B—X... 

Sinnot, M. L. (1980). Glycosyl Group Transfer. Enzyme Mechanisms. London, Royal Society of Chemistry. 259-291. 

Transferases are enzymes that transfer a chemical group, such as a methyl or glycosyl group, from one compound (the donor) to another compound (the acceptor). In many cases, the donor is a cofactor that carries the group to be transferred. A relatively large number of transferases is known (about 720), of which about 90 are available. 

Glycosyltransferases transfer glycosyl groups from a starch chain to an acceptor. The acceptor may be another starch molecule, phosphoric acid or nucleotides. Most enzymes in this class catalyze reversible reactions some enzymes are involved in the starch biosynthesis. The only glycosyltransferase responsible for starch degradation is the cyclodextrin glycosyltransferase. 

Another mechanism for the enzymic synthesis of saccharides is one that occurs through transfer of the glycosyl group from a glycosyl phosphate to an appropriate acceptor. An example of such a reaction is the synthesis of sucrose by the enzyme, sucrose phosphorylase, found in Pseudomonas saccharophila ... 

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