172 G. B. Brown 



This is work which was done in collaboration with Dr. LePage and begun 

 about two years ago. We have been studying the incorporation of 

 [2-^*C] glycine into the nucleic acids of rats. We gave these injections of 

 glycine primarily to study the incorporation by tumours, and we used 

 liver as a contrast. In addition, we separated the nucleic acids into 

 the DNA and the RNA, and we accidentally came across a rather 

 remarkable result, which has been obtained independently by Eh\yn 

 and Sprinson at Columbia, and by Totter, Volkins and Carter, and also 

 by Dr. Brown. We found an extremely high incorporation of i*C from 

 glycine into the purines of DNA, almost identical with the incorporation 

 into the purines of the RNA. These data were published as Table IV 

 in the February issue of the Journal of Biological Chemistry (J. hiol. 

 Cheryl., 1951, 188, 593). 



The isolation procedure was a modification of the Schmidt-Thann- 

 hauser technique. The RNA samples according to analysis contained 

 no DNA, and the DNA samples were contaminated with not more than 

 10 per cent of RNA. As Dr. Wilson mentioned, we found practically 

 no incorporation from glycine into thymine. The specific activities in 

 counts per minute per mg. of the RNA, adenine and guanine are 

 compared with the DNA. The specific activities for DNA are usually 

 somewhat lower than those for RNA, but they are all of the same order 

 of magnitude, whereas the data Dr. Brown had previously obtained 

 with adenine indicated a much lower incorporation, and of course the 

 work with phosphorus indicates very little turnover of ^ap in the DNA. 

 There is considerable variation from animal to animal, but our results 

 are for normal livers of so-called adult rats, which showed ample incor- 

 poration into the purines of the RNA. We also studied regenerating 

 liver, in which the incorporation was higher, and tumour, in which the 

 incorporation was generally somewhat higher than we found in normal 

 liver. This, of course was rather disturbing because of the previously 

 assumed biochemical stability of DNA and its relationship to the gene. 

 Since it has been shown by Dr. Wilson and others that the 2-carbon of 

 glycine is a precursor of the 5-carbon of the purines, and since it has 

 also been shown that glycine is converted into formate, which is a 

 precursor of the carbon in the 2 and 8 positions (the ureide positions) 

 of the purines, it seemed of some importance to degrade the purines 

 that had been obtained, since we might be observing simple exchange 

 of the ureide carbons which would result from the conversion of glycine 

 into formate. 



When the degradation is carried out by hydrolysis of the purines to 

 produce glycine, the glycine is made of the same carbons which it 

 supplied synthetically. In other words, the 5-carbon of the purine gives 

 the 2-carbon of glycine. The glycine was isolated and treated with nin- 

 hydrin to liberate formaldehyde, which was distilled, precipitated as 

 dimedon, and counted. A separate aliquot of the formaldehyde was 

 determined colorimetrically. We determined the specific activity of 

 the purines, the specific activity of the formaldehyde obtained on 

 degradation, and calculated the specific activity that the formaldehyde 

 would show if all the ^^C were present in the 5-carbon atom. These data 



