BIOSYNTHESIS OF NUCLEIC ACIDS 389 



in homogenates of pigeon liver, and that an as yet unidentified adenosine 

 phosphate, not identical with AMP, ADP, ATP, or adenosine-3 '-phosphate, 

 could contain up to 30% of the administered radioactivity. Goldwasser 

 noted'-^^ that the amount of his "ATP" fraction as determined enzymatically 

 was about one-half that indicated by the absorption at 260 m/x, and Marrian 

 recorded-'^ that his "ATP" fraction contained only a little over one easily 

 hydrolyzable phosphorus. Thus the character of the "ATP" fraction is in 

 question, which is reminiscent of the uncertainty regarding the character of 

 the ATP fractions from plant sources,^'^ and of commercial ATP prepara- 

 tions.^^^ 



The available time curves (Fresco and Marshak'^^) for the incorporation 

 of adenine into the acid-soluble and nPNA fractions in mouse liver indicate 

 that the total acid-soluble adenine does not comply with the requirements 

 for a precursor-product relationship. ^"^ The activity of the acid-soluble 

 adenine is still rising when that of nPNA has begun to decay, and the acid- 

 soluble adenine does not decay as rapidly as does the nPNA. It would ap- 

 pear^^^ that some particular component (s) of the acid-soluble fraction, with 

 an activity higher and with a shorter half-time than that of the fraction as 

 a whole, could be serving as the adenine precursor of the polynucleotides 

 and of other acid-soluble components. That the "active adenine" may be 

 converted into, and may be in equilibrium with, the larger "reservoir" of 

 adenosine-5'-phosphates is suggested by all of these experiments. 



The demonstrations'^^" that, many days after the administration of ade- 

 nine, the acid-soluble adenine of an implanted tumor, or that of an initially 

 "unlabeled" parabiotic twin, may acquire a relatively high activity al- 

 though Uttle incorporation into the polynucleotides is observed also does 

 not suggest that the total acid-soluble adenine represents an "active" 

 polynucleotide precursor. The fact that administered adenosine-5'-phos- 

 phate is only about one-half as extensively incorporated into PNA purines^^ 

 as are equimolecular amounts of the 2'- or 3 '-isomers cannot of itself be 

 interpreted to indicate that AMP is not closely related to the "active 

 adenine," since it is undoubtedly more extensively diluted and also may be 

 more susceptible to catabolism. However, that behavior also questions the 

 possibility that AMP is in rapid equilibrium with the "active" precursor. 



Recent demonstrations of the presence of highly active acid-soluble 

 guanine derivatives derived from glycine in rat liver cell suspensions, ^^^ 

 and the formation in vivo of uridine-5'-phosphates from orotic acid^^^ and of 

 a 2 , 6-diaminopurine riboside phosphate from 2,6-diaminopurine"'' also 

 indicate the rising interest in the metabolic products present in the acid- 



2'8 H. G. Albaum, M. Ogur, and A. Hirschfeld, Arch. Biochem. 27, 130 (1950). 



219 A. Kornberg, J. Biol. Chem. 182, 779 (1950). 



"0 J. Dancis and M. E. Balis, J. Biol. Chem. 207, 367 (1954). 



