Phosphorylation of sugars

There was some evidence for the possible involvement of PolyPs localized in the cell periphery in the uptake and phosphorylation of sugars as energy and phosphate donors (Van Steveninck and Booij, 1964 Hofeler et al, 1987). Later, studies of the mechanisms of transport-associated phosphorylation of 2-deoxy-D-glucose in the yeast Kluyveromyces marxianus (Schuddemat et al, 1989b) and Saccharomyces cerevisiae (Schuddemat et al, 1990) resulted in the conclusion that PolyPs seem to replenish the Pj pool and therefore had an indirect role in sugar transport. 

C. Degani and M. Halmann (1971). Mechanism of the cyanogen induced phosphorylation of sugars in aqueous solution. In R. Buvet and C. Ponnamperuma (Eds), Molecular Evolution, Vol. 

VAN BOOM Phosphorylating reagent Phosphorylation of sugars or nucleosides by means of ssflcytehloiophospite 2. 

Synthesis.—Comprehensive reviews on glycosyl esters of nucleoside pyrc>-phosphates and teichoic acids have appeared in the past year as have details of the preparation of xylulose-5-phosphate using transketolase. Phosphorylation of glucose by inorganic phosphate in the presence of histidine occurs under simulated primitive earth conditions and the reactive species is probably an iST-phosphorylated histidine. Phosphorylation of sugars by heating them with 100% phosphoric acid in vacuo is a novel experimental... 

The role of soluble, cytoplasmic enzymes in saccharide assembly seems chiefly to be in the phosphorylation of sugars and the interconversion of sugar phosphates. The enzymes of sugar nucleotide interconversion are generally membrane-associated and must, in most cases, be firmly membrane-bound. They are, therefore, likely to be integral membrane proteins and must, for the most part, be constituents of the endoplasmic reticulum. 

Oxidation by the hexose monophosphate pathway begins with the phosphorylation of sugar, followed by two successive oxidation reactions. The second is accompanied by a decarboxylation. The xylulose 5-P enters a group of transketolization and transaldolization reactions (Figure 7.2). The overall reaction is the degradation of a glucose molecule into six molecules of CO2. In parallel, 12... 

FIGURE 10.26 Glucose transport in E. coli is mediated by the PEP-dependent phosphotransferase system. Enzyme I is phosphorylated in the first step by PEP. Successive phosphoryl transfers to HPr and Enzyme III in Steps 2 and 3 are followed by transport and phosphorylation of glucose. Enzyme II is the sugar transport channel. 

Several unique features distinguish the phosphotransferase. First, phos-phoenolpyruvate is both the phosphoryl donor and the energy source for sugar transport. Second, four different proteins are required for this transport. Two of these proteins (Enzyme I and HPr) are general and are required for the phosphorylation of all PTS-transported sugars. The other two proteins (Enzyme II and Enzyme III) are specific for the particular sugar to be transported. 

The 3-deoxy pentose phosphates (44 and 45) can be further degraded to phosphorylated deoxy sugars (58) treatment of either of them with periodate will cleave the carbon-carbon bond between Ci and C2 to yield 2-deoxy-n- (46) and -L-gZycero-tetrose-4-phosphates (47). 

In another version of this method, the radical generated by radical exchange from the aryl telluride carbohydrate 83 and the N-acetoxy-2-thiopyridone affords, after intramolecular cyclization and desulfanylation, the polyhydroxylated and phosphorylated pseudo sugar 84 [54] (Scheme 23). 

The acidic sugars discussed in this Section are glycuronic acids and glycu-losonic acids. Bacterial polysaccharides may also become acidic by substitution of sugar residues, for example by etherification with lactic acid, acetala-tion with pyruvic acid, or phosphorylation, and these possibilities will be discussed in the following Sections. A sugar that does not fall into any of... 

In extrahepatic tissues, hexokinase catalyzes the phosphorylation of most hexose sugars, including fruc-... 

The complementation experiments in which the A domain of a class 111 E-II is used as the phosphoryl group donor to the B domain of a second E-II molecule with either the same or different sugar specificity, while both are fixed in a membrane matrix, raises some intriguing issues about the association state of these proteins and the kinetics of their interactions. Do E-IIs form stable homologous complexes in the membranes If so, is it necessary to postulate the formation of stable heterologous complexes to explain, for example, the phosphorylation of the B domain of E. coli 11° by the A domain of ll , or can the data be explained by assuming a... 

The physiologically relevant function of the E-IIs is vectorial phosphorylation, i.e., transport with concomitant phosphorylation of the sugar. This reaction requires a phosphoryl group donor, for instance, P-HPr, and it may even be argued that the active species is phosphorylated E-II,... 

Fig. 6. Vectorial phosphorylation by a mechanism in which translocation and phosphorylation of the sugar are two distinct steps. The product binding site of the translocator T (domain C of II ") would be the substrate binding site of the kinase K (domains A and B). Since both the left-hand cycle and the right-hand cycle are catalyzed by the same enzyme they will very likely be kinetically dependent. Note that the kinetic cycle on the left-hand side of the figure is identical to Fig. 5.

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