Sugars phosphorylated

The 3-deoxy 1,2-O-isopropylidene D-gluco- (37) and D-galacto-furanoses (17) have been used (53, 58) in yet another way to prepare deoxy sugars phosphorylated in the terminal position. If either of these compounds is treated with one molar equivalent of periodate, carbon 6... 

More recent kinetic data indeed indicate that the kinetics of sugar phosphorylation is more complicated than originally thought. A kinetic scheme that explains the data may have to include all or some of the items listed above. In the following section two such schemes will be discussed. Firstly, a scheme based upon the kinetic performance... 

Fig. 10. Mechanisms of steady-slqte kinetics of sugar phosphorylation catalyzed by E-IIs in a non-compartmentalized system. (A) The R. sphaeroides 11 model. The model is based on the kinetic data discussed in the text. Only one kinetic route leads to phosphorylation of fructose. (B) The E. coli ll " model. The model in Fig. 8 was translated into a kinetic scheme that would describe mannitol phosphorylation catalyzed by Il solubilized in detergent. Two kinetic routes lead to phosphorylation of mannitol. Mannitol can bind either to state EPcy, or EPpe,. E represents the complex of SF (soluble factor) and 11 and II in A and B, respectively. EP represents the phosphorylated states of the E-IIs. Subscripts cyt and per denote the orientation of the sugar binding site to the cytoplasm and periplasm, respectively. PEP, phosphoenolpyruvate.

Deoxyadenosine is a related nucleoside. It contains deoxyribose instead of ribose as the sugar. Phosphorylation of deoxyadenosine produces a nucleotide found in DNA. 

However, the situations may become more sophisticated if uptake systems with stronger links to the nonlinear network dynamics are considered. The important example of the phosphoenol-dependendent phosphotransferase system (PTS) in Escherichia coli is discussed next to illustrate this level of complexity. The reaction scheme shown in Fig. 23 is responsible for the concomitant translocation and phosphorylation of several sugars across the cyto-plasmatic membrane. Sugar phosphorylation and translocation of glucose appears to involve several phosphoproteins, intermediates, and phosphoryl transfer reactions. 

Transferases 750 -100 Transfer of groups aldehydic, ketonic, acyl, sugar, phosphoryl, methyl, NH3 ++... 

Methods have been developed to reveal the presence and the position of phosphate ester moieties on sugars. Phosphorylated sugar constituents, e KDO, heptoses and glucosamine, in bacterial polysaccharides were detected by comparison... 

The PTS catalyzes group translocation, the coupling of sugar transport to sugar phosphorylation. Phosphoenolpyruvate is the initial phosphoryl donor. It phosphorylates Enzyme L and then the phos-phoryl group is sequentially passed to HPr, Enzyme DA, Enzyme IIB, and finally to an incoming sugar... 

Phosphorus. Eighty-five percent of the phosphoms, the second most abundant element in the human body, is located in bones and teeth (24,35). Whereas there is constant exchange of calcium and phosphoms between bones and blood, there is very Httle turnover in teeth (25). The Ca P ratio in bones is constant at about 2 1. Every tissue and cell contains phosphoms, generally as a salt or ester of mono-, di-, or tribasic phosphoric acid, as phosphoHpids, or as phosphorylated sugars (24). Phosphoms is involved in a large number and wide variety of metaboHc functions. Examples are carbohydrate metaboHsm (36,37), adenosine triphosphate (ATP) from fatty acid metaboHsm (38), and oxidative phosphorylation (36,39). Common food sources rich in phosphoms are Hsted in Table 5 (see also Phosphorus compounds). 

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. 

FIGURE 10.27 The path of the phosphoryl group through the PTS mechanism. Reactive phosphohistidine intermediates of Enzyme I, HPr, and Enzyme III transfer phosphoryl groups from PEP to the transported sugar. 

Another simple sugar that enters glycolysis at the same point as fructose is mannose, which occurs in many glycoproteins, glycolipids, and polysaccharides (Chapter 7). Mannose is also phosphorylated from ATP by hexokinase, and the mannose-6-phosphate thus produced is converted to fructose-6-phosphate by phosphomannoisomerase. 

A somewhat more complicated route into glycolysis is followed by galactose, another simple hexose sugar. The process, called the Leloir pathway after Luis Leloir, its discoverer, begins with phosphorylation from ATP at the C-1 position by galactokinase ... 

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