IV. BIOCHEMICAL SYSTEMS 127 



gi-owtli. Similar results were obtained with S.faecalis using both "x methyl 

 PGA" and N'"-methylpteroic acid as antagonists (Slokstad ci alJ). In this 

 case the antagonist had no effect, even at liigh concentrations when l)oth 

 adenine and thymine were supplied. These results with N^^-methylpteroic 

 acid are shown in Table IT. This indicates that the onlj^ function of PGA in 

 S. faecalis is purine and pyrimidine synthesis and is in contrast to the situa- 

 tion in L. casei where PGA has a third additional role. 



TABLE II 



Effect of Adenine and Thymine on Inhibition Ratio of N-Mp:thyl Pteroic 



Acid — Organism: S. faecalis R (Stokstad et al.'') 



2. SuLFONA^UDE, p-AMINOBENZOIC AciD, AND PuRIXE ReL.^TIONSHIPS 



An interesting relationship between p-aminobenzoic acid and the metab- 

 olism of purines, amino acids, and pyrimidines has been shown in E. coli 

 h\ inhibition studies with sulfanilamide. 



Shive and his associates^- ^ and Winkler and de Haan^" have shown that 

 sulfanilamide, in progressively higher concentrations, inhibits successively 



' E. L. R. Stokstad, M. Regan, A. L. Franklin, and T. H. Jukes, Federation Proc. 7, 

 193 (1948). 



8 W. Shive and E. C. Roberts, /. Biol. Chem. 162, 463 (1946). 



9 W. Shive, Ann. N. Y. Acad. Sci. 52, 1212 (1950). 



" K. C. Winkler and P. G. de Haau, Arch. Biochem. 18, 97 (1948). 



