Glycosyl nucleotides primary

In conclusion, it may be stated that present knowledge of the enzymic mechanisms catalyzing the formation of heteroglycans from glycosyl-nucleotides as glycosyl donors, and of the relevance of such synthetic mechanisms to the formation of the intact, primary cell-wall, is very limited. In particular, no heteroglycan having properties identical to those of known, native polymers of the primary wall has yet been synthesized in vitro. 

It has been suggested12 that a distinction be made between the primary and the secondary glycosyl nucleotides. The former derivatives are produced as a result of the interaction of nucleoside 5 -triphosphates with glycosyl phosphates for nucleoside glycosyl diphosphates) or monosaccharides (for cytidine glycosyl monophosphates). The enzymes that catalyze these reactions belong to the group of nucleotidyltransferases... 

EC 2.7.7 group). Secondary glycosyl nucleotides are formed from the primary derivatives through enzymic reactions leading to modification of their monosaccharide fragments these conversions are discussed in Section III. 

In bacteria, primary glycosyl nucleotides include14 22 UDP-Glc, as well as other nucleotide derivatives of the same monosaccharide. Important representatives of this class are16"21,23"25 dTDP-Glc and17"19,21,26 29 CDP-Glc, which serve as precursors for a number of secondary glycosyl nucleotides, whereas similar enzymic reactions have not been demonstrated for GDP-Glc,1819,21,30 and ADP-Glc17 19,21-31"38 seems to participate only in the biosynthesis of bacterial glycogen, a subject that is beyond the scope of this article. 

Guanosine (D-mannosyl diphosphate) (GDP-Man, 4)39-42 and uridine (2-acetamido-2-deoxy-D-glucosyl diphosphate) (UDP-GlcNAc, 5)43,44 are other important examples of primary glycosyl nucleotides. Although formation of ADP and dTDP derivatives of the latter monosaccharide was observed,17 their functions remain obscure.45... 

The symbol X in the Table means that an activated form of the monosaccharide is not known a dash shows that the monosaccharide has not been identified as a component of bacterial polysaccharides. For references, see the text. 6 See Ref. 101 for abbreviations. c Primary glycosyl nucleotide. 4 See comments in the text. 

The key intermediates in the biosynthesis of 6-deoxy sugars are the nucleoside 6-deoxyhexosyl-4-ulose diphosphates (7), formed through enzymic reactions catalyzed by NDP-sugar 4,6-dehydratases (EC 4.2.1.45-47) from primary glycosyl nucleotides. These reactions were observed... 

In this group of monosaccharide components of bacterial polysaccharides, a primary glycosyl nucleotide is ADP-D-g/ycero-D-manno-heptose (9), identified in extracts of a mutant strain of Shigella sonnei.231... 

Aldose-l-phosphates synthesized by the reaction of aldoses with ATP or by isomerization of sugar-co-phosphates are the primary glycosides. They may act as glycosyl donors in the synthesis of other glycosides either directly or after transformation to nucleotide-diphosphate sugars (C 6). 

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