GlcNAc-phosphate

Peripheral to the Gal-GlcNAc sequences of glycoproteins, there can occur an array of blood-group-related glycosylations, anionic substitutions (sialy-lation, 0-sulfation, and 0-phosphorylation), or both. Chains of the high-mannose type may also bear phosphate groups. Table VI reviews the pat-... 

UDP-GlcNAC enolpyruvyltransferase (MurZ) catalyzes the reaction between the phosphate of the enol pyruvate and the UDP-GlcNAC to form the corresponding enolpyruvate. This reaction is the first stage of the biosynthesis of the peptidoglycan of the bacterial wall. Phosphates of mono- and difluoroenolpyruvates are substrates of MurZ (Figure 7.30). The tetrahedral intermediates formed after incubation... 

The enzymes catalyzing these reactions are membrane-bound, and are stimulated by exogenous dolichol phosphate. It has been suggested, and now shown43 (at least in the formation of GlcNAc-PP-Dol by enzymes from yeast), that Dol-P stimulates the incorporation of sugar residues into the lipid intermediates because it serves as a substrate. 

From bisubstrate, kinetic analysis with a transferase from hen oviduct that, under the conditions of the assay, formed only GlcNAc-PP-Dol, it followed that both dolichol phosphate and UDP-GlcNAe have to he bound to the enzyme before release of the product occurs.52 However, the fact that only partially purified preparations have thus far been obtained (the preparations may also still be contaminated with substrates and product), together with experimental difficulties in handling both the substrate dolichol phosphate (which, furthermore, is not one compound, see the earlier discussion) and the unstable enzyme (enveloped in micelles of detergent), make difficult a sensible interpretation and comparison of the kinetic parameters detenuined for the different enzvme-preparations. The solubilized enzymes catalyzing reactions 1,2, and 3 have in common their alkaline pH optima and dependence on Mg2+ or Mn2+ ions. The latter fact makes (ethylenedinitrilo)tetraacetic acid (EDTA) a reversible inhibitor of enzyme activity and an important experimental tool. 

In eukaryotic cells, amphomycin inhibits the formation of GlcNAc-PP-Dol, Man-P-Dol, and Glc-P-Dol from their respective nucleotide esters of sugars and Dol-P.134,158,347,348 These reactions have in common the fact that they require manganese ions and Dol-P, but high concentrations of neither the ion nor the lipid phosphate were able to overcome these blocks. The transfer of preformed Man-P-Dol347 (and, pos-... 

Fig. 4.3.2 Human sialic acid metabolism and genetic defects. -6P -6-Phosphate, -9P -9-phos-phate, CMP cytidine 5 -monophosphate, CTP cytidine 5 -triphosphate, UDP-GlcNAc uridine diphosphate-N-acetyl-D-glucosamine, ManNAc N-acetylmannosamine, NeuAc N-acetylneur-aminic acid, OGS oligosaccharides, SASD sialic acid storage disease...

CDG-Ij UDP-GlcNAc dolichol phosphate N-acetylglucos-aminephosphotransferase 1 DPAGT1 1 lq23 608093... 

One of the compounds formed from UDP-GlcNAc is UDP-N-acetylmuramic acid. The initial step in its synthesis is an unusual type of displacement reaction on the a-carbon of PEP by the 3-hydroxyl group of the sugar (Eq. 20-6, step a).40410 Inorganic phosphate is... 

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