Sugar phosphates, hydrolysis

RNA is relatively resistant to the effects of dilute acid, but gentle treatment of DNA with 1 mM HCl leads to hydrolysis of purine glycosidic bonds and the loss of purine bases from the DNA. The glycosidic bonds between pyrimidine bases and 2 -deoxyribose are not affected, and, in this case, the polynucleotide s sugar-phosphate backbone remains intact. The purine-free polynucleotide product is called apurinic acid. 

Sugar The hydrolysis of sucrose in the intestine produces both glucose and fructose, which are transported across the epithelial cells by specific carrier proteins. The fructose is taken up solely by the liver. Fructose is metabolised in the liver to the triose phosphates, dihydroxy-acetone and glycer-aldehyde phosphates. These can be converted either to glucose or to acetyl-CoA for lipid synthesis. In addition, they can be converted to glycerol 3-phosphate which is required for, and stimulates, esterification of fatty acids. The resulting triacylglycerol is incorporated into the VLDL which is then secreted. In this way, fructose increases the blood level of VLDL (Chapter 11). 

Chapters 17 through 21 deal with carbohydrate-enzyme systems. Hehre presents some new ideas on the action of amylases. Kabat presents some new immunochemical studies on the carbohydrate moiety of certain water-soluble blood-group substances and their precursor antigens. Hassid reviews the role of sugar phosphates in the biosynthesis of complex saccharides. Pazur and co-workers present information obtained by isotopic techniques on the nature of enzyme-substrate complexes in the hydrolysis of polysaccharides. Gabriel presents a common mechanism for the production of 6-deoxyhexoses. An intermediate nucleoside-5 -(6-deoxyhexose-4-ulose pyrophosphate) is formed in each of the syntheses. 

One of the simplest methods of estimation of PolyPs in extracts is based on the assay of Pi, which is released from the PolyPs by hydrolysis with 1 M HC1 at 90 °C for 10 min. The Pi released under these conditions is defined as labile phosphorus . If the compounds containing organic labile phosphorus (i.e. nucleotide phosphates, sugar phosphates, etc.) were removed from the extracts by adsorption on Norit charcoal, the increase in Pj content after hydrolysis can be attributed to PolyP and pyrophosphate (PPi). Estimation of the PPj content (Mansurova, 1989) before hydrolysis may be needed in some cases for more precise calculations of the PolyP content. Pi may be determined by one of the well-known chemical methods (Fiske and Subarrow, 1925 Weil-Malerbe and Green, 1951). 

Phosphorus is essential to all living systems. Within biological systems the most abundant forms of phosphorus are phosphate diester bonds, which form the links within nucleic molecules. Phosphate is an indispensable portion of the ATP molecule. The hydrolysis of phosphate from ATP to ADP forms the basis of most energy transfer reactions within biological systems. Phospholipids and sugar phosphates are constituents of all living cells. 

Treatment of SXIA, after the consumption of one mole of periodate per mole, with phenylhydrazine, followed by acidic hydrolysis, yields a sugar phosphate which, on enzymic dephosphorylation, gives glucose. A galacto-sylerythritol is obtained from a Smith degradation of reduced, alkali-degraded SXIA. 

The reactions of transition-metal complexes with polynucleotides generally fall into two categories (i) those involving a redox reaction of the metal complex that mediates oxidation of the nucleic acid and (ii) those involving coordination of the metal center to the sugar-phosphate backbone so as to mediate hydrolysis of the polymer. Both redox and hydrolytic reactions of metal complexes with nucleic acids have been exploited with much success in the development of tools for molecular biology. 

Last, it must be mentioned that metal coordination to the purine N7 position can also indirectly promote strand cleavage, although not through direct hydrolytic reaction on the sugar-phosphate backbone. Metal ions such as Pd and Cu, through coordination at N7, promote depurination. The depurinated site then becomes easily susceptible to hydrolysis upon treatment with mild base. 

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