Nucleic acids isotope incorporation

Most of the early methods for assigning isotopically labeled nucleic acids were developed using RNA samples, since 13C and 15N isotopes can be incorporated in RNA more easily than in DNA. While most of the magnetization transfer pathways in RNA and DNA are the same, the latter contains thymine rather than uracil. To remove the ambiguity of intra- and inter-residue H6-CH3 peak assignment in thymine, the HCCCH through-bond method was proposed [51] as a more sensitive alternative to NOE or ROE. 

Changes in the rate of synthesis of nucleic acids as measured by the rate of incorporation of labeled precursors may be more informative than changes in nucleic acid concentrations in atrophying muscle. An enhanced incorporation of isotope into nucleic acids after glycine- C is administered to dystrophic mice (aged % to 2 months) was found by Coleman and Ashworth (Cl) the free glycine pool was the same in normal and dystrophic muscle. More extended studies have been reported by Srivastava (S14), who used uridine-2- C as a precursor of RNA. At 30 days of age the incorporation in the dystrophic muscle was higher than normal, but it was the same at 60 days and lower at 90 days. These differences were confirmed by in vitro incorporation experiments... 

Bone GJ, Steinert M. Isotopes incorporated in the nucleic acids of Trypanosoma mega. Nature 1956 178(4528) 308-309. 

You are to study kinetic parameters of nucleotide incorporation in a growing nucleic acid chain. Which of the hydrogen isotopes - deuterium or tritium - will you use and why ... 

Adenine is inert in the nucleoside phosphorylase systems of both mammalian tissues and microorganisms, but isotopically labeled adenine is effectively incorporated into nucleic acid purines, both in rats " and in yeast.This poses a question as to the possible role of nucleoside phosphorylase in polynucleotide synthesis. It has been suggested that hypoxanthine or guanine nucleosides (or nucleotides) are synthesized first. Then an exchange reaction with free adenine (or a derivative) might occur, For example, adenine might react with inosine to form adenosine and hypoxanthine. Some known exchange reactions are discussed below. 

Fortunately, my graduate research in biochemistry at Baylor College of Medicine, in Houston, involved studies on the mechanism of formic acid oxidation in animal tissues and on the incorporation of this one-carbon compound into nucleic acid components and their precursors. This provided me with experience in the use of isotopic tracers and the background in biochemical research which proved crucial, in later years, for unraveUng the intermediates and mechanisms of synthesis of purines and other compounds, when I discovered the prebiotic synthesis of adenine and other building blocks of nucleic acids, and a general pathway or method for the prebiotic formation of oligodeoxynucleotides and peptides. 

Thus, cleavage to adenine was not the explanation for the incorporation of either inosine or adenosine into the nucleic acids. If a small amount of free adenine was formed, isotope should have appeared in the 2,8-dioxyadenine deposited in the kidney. 

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