384 GEORGE BOSWORTH BROWN AND PAUL M. ROLL 



rines. However, since adenosine is more extensively anabolized than is inosine (in 

 both the rat^' and in L. casei^^), there must be some direct anabolism of it. Adenosine 

 phosphokinase^" ''8^ will bring about a phosphorylation of adenosine or of 2,6-di- 

 aminopurine riboside in the 5'-position, and offers a possible anabolic route for those 

 nucleosides. 



The question of whether the nucleoside phosphorylase (Chapter 24) normally 

 plays a synthetic role remains unanswered. In in vitro studies it has been demon- 

 strated that this equilibrium may be far toward the synthetic side. This enzyme is 

 effective with the nucleosides of hypoxanthine or guanine, the purines of which are 

 not utilized by the rat (although guanine can be utilized by many species), but it 

 has not been demonstrated to effect adenosine. Kalckar'^ has pointed out that, if 

 purine nucleoside phosphorylase is capable of catalyzing a transfer of ribose from 

 ribose-1 -phosphate to adenine or to 2,6-diaminopurine, the detection of such a re- 

 action would be difficult if the equilibrium were much less favorable than that with 

 hypoxanthine or guanine. It was reported"^ that calf liver extracts are able to cat- 

 alyze the formation of a purine nucleotide from ribose phosphate (from yeast adenylic 

 acid) and adenine, guanine, or hypoxanthine, but not from xanthine. Consideration 

 of the possibility of an incorporation in the mammal of purine nucleosides via a type 

 of transglycosidation'^ with nucleotides must await information as to whether the 

 ribose of purine nucleosides behaves like that of cytidine*^ and accompanies the 

 purine into polynucleotides. 



An indication of some lack of specificity of some of the enzymes dealing with the 

 anabolism of nucleic acid components is suggested by the incorporation of 5-bromo- 

 uracil into the polynucleotides of Streptococcus faecalis^^^ and Enterococciis ,^^'' and 

 that of azaguanine into mouse, '^* T. geleii^^^ or plant virus nucleic acids,''" the latter 

 case including a definite demonstration of its incorporation into glycosidic linkage. 

 2,6-Diaminopurine has been demonstrated to be incorporated into an acid-sol- 

 uble phosphate of 2,6-diaminopurine riboside."" 



3. Polynucleotide Synthesis in L. casei 



In this microorganism, an overall pattern of the utilization of many- 

 labeled purine derivatives has been elaborated.^- •^^■^''•^''•^^ There is no 

 evidence of degradation of purines by this organism,^" and the total quantity 

 of the purine consumed during growth can approximate that found in the 

 cells produced, so the use of the growing microorganism presents a system 

 in which the results represent almost exclusively the synthetic phase of 

 nucleic acid metabolism. 



Under conditions which will allow synthesis de novo and where the added 

 purine does not further stimulate growth (in media containing folic acid), 



184 R. Caputto, J. Biol. Cheyri. 189, 801 (1951). 



185 J. Wajzer and F. Baron, Bull. soc. chim. biol. 31, 750 (1949). 



186 Y. Weygand, A. Wacker and H. Dellweg, Z. Naturforsch. 7b, 19 (1952). 

 '" F. Weygand and A. Wacker, Z. Naturforsch. 7b, 26 (1952). 



188 J. H. Mitchell, Jr., H. E. Skipper, and L. L. Bennett, Jr., Cancer Research 10, 647 



(1950). 

 •89 M. R. Heinrich, V. C. Dewey, R. E. Parks, Jr., and G. W. Kidder, J. Biol. Chem. 



197, 199 (1952). 

 ISO R. E. F. Matthews, Nature 171, 1065 (1953). 



