Nucleotides, as tissue constituents

The discovery of a large number of nucleotides as normal tissue constituents, and their separation, isolation, and characterization (Chapter 1), their structures in solution (Chapter 2), and a general discussion of the many and varied functions of nucleotides in cells (Chapter 3), provide a background and general framework for the discussion of the syntheds, inter conversion, and catabolism of these natural products which follows in later chapters. 

In experiments of this type with animal tissues, Rose and Schweigert (2) and Thomson et al. (S) showed that pyrimidine ribonucleosides were converted to DNA nucleotides without cleavage of the JNT-glycosidic bond. As well, Larsson and Neilands (4) performed a similar type of experiment in which P-phosphate and uniformly labeled C-cytidine were administered to rats with regenerating liver. Both substances were incorporated into the liver polynucleotides which, upon isolation, were degraded to their constituent nucleotides for analysis. Their data (Table 16-1) showed that the four nucleotides of RNA had similar specific activities with respect to P, indicating that the labeled phosphate readily equilibrated with the nucleoside phosphate pool during the experimental period. In this experiment, cytidylate derived from RNA and deoxycytidylate derived from DNA had the same P C ratio. This result indicated that both polynucleotide subunits, deoxycytidylate and cytidylate, were derived from a common precursor, evidently a ribonucleotide. 

The problem of non-RNA organic phosphorus compounds as contaminants in the RNA fraction has been studied by Mauritzen and Stedman (75) in connection with their RNA analyses of isolated cell nuclei, where this constituent is present in very small quantities. They present extensive data concerning the degree of contamination of the RNA nucleotides with organic and inorganic phosphates following the alkaline d estion, in the ST or STS procedure, of nuclear nucleic acids. They concluded that, for accurate assay of RNA in these methods, it is necessary to convert the pentose in the RNA fraction to furfural (5,33) with acid digestion, and assay the distilled furfural by the formation of a colored product with aniline acetate. Similar data on this type of contamination of various tissue fractions is presented by Davidson and Smellie (32) (see Section II, 1, F). 

Nicotinic amide, C H4N.CO.NH2, is a constituent of the coenzymes, co-dehydrase I and II, and as such acts as a hydrogen carrier in tissue respiration. The amide is derived from nicotinic acid, or carboxy pyridine, and is combined with ribose phosphate and adenosine in nucleotide structure in the co-dehydrases. Its hydrogen-carrying power is due to the reducibility of the onium nitrogen in the pyridine ring (p. 258). 

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