STUDIES WITH ORGANIC- AND BIO-SYNTHETIC 

 NUCLEOSIDES AND NUCLEOTIDES 



G, B. BROWN* 



Of nine labelled purines thus far studied only two have 

 been found to be utilized by the rat for the synthesis of nucleic 

 acids: adenine (Brown, Roll, Plentland Cavalieri, 1948) which 

 may serve as a precursor of both adenine and guanine of the 

 polynucleotides, and 2,6-diaminopurine (Bendich and Brown, 

 1948) which leads only to polynucleotide guanine. The 

 earlier studies of Plentl and Schoenheimer (1944) with 

 [2-amino-l,3-^^N3] guanine showed that it was not utilized by 

 the rat to a significant extent and this conclusion was later 

 affirmed in our laboratory. It was subsequently demonstrated, 

 however, that this guanine could be utilized by the C57 black 

 mouse to an appreciable degree (Brown, Bendich, Roll and 

 Sugiura, 1949). 



In view of this utilization of guanine by the mouse, and 

 also its extensive utilization by yeast (Kerr, Seraidarian and 

 Brown, 1951) and Lactobacillus casei (Balis, Brown, Elion, 

 Hitchings and Vanderwerff, 1951), the fate of guanine in the 

 Sherman rat was reinvestigated with highly active [8-^*C] 

 guanine. This more sensitive tracer not only permitted 

 detection at a greater dilution but also avoided the general 

 contribution of ^^NHg to body pool ammonia which obscured 

 any small specific incorporation of the intact purine. This 

 ^*C labelled guanine was incorporated into the pentose poly- 

 nucleotide guanine of the rat at a 1:1,000 dilution (Balis, 

 Marrian and Brown, 1951), which is about one per cent of the 



♦The author wishes to express appreciation to the several collaborators 

 responsible for the studies summarized here and for the support of the National 

 Cancer Institute of the United States Public Health Service, Tlie United 

 States Atomic Energy Commission, Contract AT (30-l)-910, The Nutrition 

 Foundation, Inc., and the James Foundation of New York, Inc. 



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