IV NUCLEIC ACIDS AND NUCLEO PROTEINS 909 



precursors into nucleic acid purines in heterologus implants of human tumors and 

 in the livers and intestines of hamsters and rats treated with cortisone (Bennett 

 et al., 1956). The human tumor explants exhibited de novo synthesis of nucleic acid 

 purines. Guanine and hypoxanthine were not utilized to any significant extent. 

 The tumors incorporated adenine to approximately the same extent as normal 

 tissues. Diaminopurine was found to be a good precursor of nucleic acid guanine 

 in the tumors, relative to normal tissues. 



(ii) Nucleosides and nucleotides. Nucleotides were isolated from the acid-soluble 

 fraction of normal and tumor tissues in animals previously injected with glucose- 

 i-'^^C (Schmitz et al., 1954). Also, the mono-, di- and triphosphates of cytidine, 

 guanosine, uridine and adenosine were isolated from the acid soluble fraction of 

 Flexner-Jobling carcinoma (Schmitz et al., 1955). These studies did not indicate 

 the presence of a different metabolic or compositional pattern for tumor tissues. 

 Daoust and Cantero (1955) determined the specific activity of the acid soluble 

 nucleotides in rat liver, intestinal mucosa, and hepatoma following the adminis- 

 tration of ^^P. The incorporation of the -^^P into the nucleotides was rapid, but 

 occurred at approximately the same rate in the liver, liver tumor or intestinal 

 mucosa. Etinghof and Balyasnaya (1953) have investigated the metabolism of 

 inosinic acid in ascites tumor cells. 



Glycine-2-^'*C and -^^P were injected simultaneously by the intraperitoneal 

 route into normal rats and rats bearing Flexner-Jobling carcinoma. These animals 

 were sacrificed at various time intervals and the livers and tumors were fraction- 

 ated by the sucrose method. Nucleic acids from the various fractions were hydro- 

 lyzed and the nucleotides separated by ion exchange chromatography (Tyner 

 et al., 1953). The phosphorus specific activity was measured, the purine nucleo- 

 tides were further hydrolyzed and the ^''C specific activity of the purines was 

 ascertained. The specific activity of the DNA and RNA nucleotides in tumors 

 was higher at all times than in the corresponding liver nucleotides. Specific 

 activities of the ^-^P and '^C in the purine nucleotides from DNA were of the 

 same magnitude. However, the specific activity of the -^^P in the RNA purine 

 nucleotides of liver was higher than that of ^"^C. This would indicate that the 

 phosphorus was incorporated into an intermediate precursor earlier than was 

 the glycine. The nuclear RNA of both liver and tumors contained more radio- 

 activity than the cytoplasmic fraction at early time intervals following the adminis- 

 tration of the labeled components. This high metabolic activity of the nuclear RNA 

 confirms the observations of several other investigators. In general, Tyner et al. 

 (1953) were of the opinion that the nucleic acid metabolism of tumors was c^ualita- 

 tively similar but quantitatively more rapid than that of liver. Quantitative differ- 

 ences in the extent of labeling of nucleic acids of liver or hepatoma were observed 

 by Werkheiser and Visser (1955). Following the addition of formate-'^'C, the 

 purine nucleotides from hepatoma RNA contained several times more ^'^C than 

 the corresponding fraction from normal liver. The uridylic acid from the tumor 

 was approximately twice as active as the liver uridylic acid after the injection 

 of carbamyl aspartate-^'^C. The extent of labeling of the cytidylic acid was con- 

 siderably lower than that of the uridylic acid in both tissues. Aminouridine greatly 



Literature p. p/51 



