DEOXYPENTOSE NUCLEIC ACIDS 11 



much more resistant. For this reason, we turned to the hydrolysis 

 of the pyrimidine nucleotides by means of concentrated formic 

 acid. For the Hberation of the purines, N sulfuric acid (100°, 

 1 h) is employed; for the liberation of the pyrimidines, the 

 purines are first precipitated as the hydrochlorides by treatment 

 with dry HCl gas in methanol and the remaining pyrimidine 

 nucleotides cleaved under pressure with concentrated formic acid 

 (175°, 2 h). This procedure proved particularly suitable for the 

 investigation of the deoxypentose nucleic acids. For the study of 

 the composition of pentose nucleic acids a different procedure, 

 making use of the separation of the ribonucleotides, was devel- 

 oped more recently, which will be mentioned later. 



7. COMPOSITION OF DEOXYPENTOSE NUCLEIC ACIDS 



It should be stated at the beginning of this discussion that the 

 studies conducted thus far have yielded no indication of the oc- 

 currence in the nucleic acids examined in our laboratory of 

 unusual nitrogenous constituents. In all deoxypentose nucleic 

 acids investigated the purines were adenine and guanine, the 

 pyrimidines cytosine and thymine. The occurrence in minute 

 amounts of other bases, e.g., 5-methylcytosine, can, however, 

 not yet be excluded. In the pentose nucleic acids uracil occurred 

 instead of thymine. 



A survey of the composition of deoxyribose nucleic acid ex- 

 tracted from several organs of the ox is provided in Table 2 

 (Ref. 29). The molar proportions reported in each case represent 

 averages of several hydrolysis experiments. The composition of 

 deoxypentose nucleic acids from human tissues is similarly il- 

 lustrated in Table 3 (Ref. 30). The preparations from human 

 liver were obtained from a pathological specimen in which it was 

 possible, thanks to the kind cooperation of Dr. M. Faber, to 

 separate portions of unaffected hepatic tissue from carcinom- 

 atous tissue consisting of metastases from the sigmoid colon, 

 previous to the isolation of the nucleic acids. 



In order to show examples far removed from mammalian 



References p. 23 



