Desoxyribose nucleoside

These reactions have been described by Friedkin and Kalckar and by Manson and Lampen - the desoxynucleoside phosphorylase will be discussed in greater detail in the chapter, Nucleotides and Nucleosides. Desoxyribose-5-phosphate has been generated from the nucleoside, and Hoffmann and Lampen have proceeded to the study of the degradation of desoxyribose phosphate in E. 

This procedure gave the desoxyribose nucleosides of guanine, cytosine, thymine, and hypoxanthine. It was later discovered by Klein that the desoxyribosylhypoxanthine had been formed from desoxyribosyladenine by the action of a deaminase of the intestine. He found that silver ions selectively inhibit this deaminase, and so was enabled to isolate the adenine nucleoside. 

In 1935, Levenc and Tipson established the furanose structure of thymidine and suggested that the other nucleosides of desoxyribose-nucleic acid are likewise furanose. On this assumption the phosphoryl groups must be situated at positions (3) and (5), and they therefore suggested " the following formula for the tetranucleotide of desoxyribose-nucleic acid. 

F9. Friedkin, M., and Kalckar, H. M., Desoxyribose-1-phosphate. I. The phosphoroly-sis and resynthesis of purine desoxyribose nucleoside. J. Biol. Chem. 184, 437-449 (1950). 

L. A. Manson and J. O. Lampen, Some chemical properties of desoxyribose nucleosides, ]. Biol. Chem., 191 (1951) 87-93 For a review of applications involving nucleosides and nucleic acids, see G. Schmidt, Periodate oxidation of ribonucleic acids and their derivatives. Methods Enzymol, 12, (1968) 230-235. 

Nucleosides consist of (1) a purine or pyrimidine, which is responsible for the high characteristic ultraviolet absorption (2) a pentose, which is either ribose or desoxyribose. The structural formulas of adenosine (I), guanosine (II), uridine (III), and cytidine (IV) are given below. 

The furanose form of D-ribose is required for the enzymatic phosphorolysis reaction. Pyranose-ribose-l-phosphate will not react with hypoxanthine to liberate inorganic phosphate. On the other hand, desoxyribose nucleosides are quite reactive ... 

Desoxyribose-l-phosphate has been obtained as the crystalline cyclo-hexylamine salt. It is even more acid-labile than ribose-l-phosphate. Thus, 50% of the phosphorus is released as inorganic phosphate within 10 to 15 minutes upon hydrolysis at pH 4, at 23°C. The equilibrium favors synthesis. It is felt that the same enzyme catalyzes the phosphorolysis of hypoxanthine riboside and hypoxanthine desoxyriboside, because the Michaelis-Menten constants are nearly identical and there is no summation of rates with both substrates present at optimal concentrations. Furthermore, nucleoside phosphorylase purified from horse liver is active with both nucleosides and desoxynucleosides. ... 

The desoxyribose-5-phosphate generated enzymatically as described above has been converted to hypoxanthine desoxyriboside in extracts of E. coli in two reactions, analogous to the phosphoribomutase and nucleoside phosphorylase reactions. These are ... 

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