170 G. B. Brown 



with the relative incorporation into the PNA and into the 

 DNA cytosines being in the ratio of about 2 to 1. The con- 

 trast between that extent of the conversion of the pyrimidine 

 derivative and a corresponding ratio of about 8 or 10 to 1 

 for the purine derivatives may have a bearing on another of 

 the currently perplexing problems in nucleic acid metabolism. 

 The above observations, in conjunction with the facts that 

 DNA purines are not derived from adenine (Furst, Roll and 

 Brown, 1950) to the extent that they are derived from glycine 

 (Bergstrand et al., 1948; Elwyn and Sprinson, 1950; LePage 

 and Heidelberger, 1951), formate (Totter et al., 1950) and 

 cytidine (Hammarsten and Reichard, 1950) may be related 

 in some as yet obscure manner. The implication that the 

 deoxyribosenucleic acid purines arise by pathways perhaps 

 quite different from those for the ribosenucleic acid purines 

 suggests that studies with purine deoxyribonucleotides are 

 urgently needed. 



Another instance of marked dissimilaritv of results obtained 

 with different precursors is found in the relative incorporation 

 of [1,8-^^X2] adenine and ^^C-formate into various organs. 

 Orally administered adenine is incorporated into liver, kidney, 

 intestine, spleen, testis in that decreasing order (Furst et aL, 

 1950), with the ratio of the incorporation into liver and intes- 

 tine being somewhat less than 2 to 1. The incorporation of 

 intraperitoneally administered formate into the adenine of 

 the pentose nucleic acids of various organs was in the order : 

 intestine, kidney, spleen, liver, pancreas, testis; with a liver 

 to intestine ratio of • 16 to 1 (Marrian, Drochmans, unpub- 

 lished). In connection with another experiment, [1,8-^^X2] 

 adenine and ^*C-formate were administered simultaneously by 

 intraperitoneal injection (GoldthAvait, Bendich, unpublished) 

 and, in confirmation of the separate experiments mentioned 

 above, the liver to intestine ratios were 1 • 6 to 1 for the incor- 

 poration of adenine and 0-25 to 1 for the incorporation of 

 formate. This preferential incorporation of a purine into 

 liver nucleic acids and of a purine precursor into those of 

 intestine adds to the complications and points up the necessity 



