IV. BIOCHEMICAL SYSTEMS 



129 



fi;;misms either iu cells grown on vitamin-deficient media or with PGA 

 antagonists. However, in studies with sulfanilamide inhibition of E. coli 

 a compound, 4-amino-5-imidazolecarboxamide, was obtained which ap- 

 pears to be an intermediate in purine synthesis. The existence of this 

 compound was first noted by Stetten and Fox/^ who observed that E. coli 

 grown in a synthetic medium containing amino acids and a bacteriostatic 

 concentration of sulfadiazine produce a diazotizable amine. The formation 



NH, 



Metliionine 



5(4)-Amino-4l,o)-iniidazolecarbox- 

 aniide (,or derivative) 



^^ 



Hypoxanthine 

 Xanthine 

 CH Adenine 

 Guanine 

 or derivatives 

 Hypoxanthine 



' 

 II 

 NH;-CH,-C-OH 



Glycine 



OH NHj 

 I I 



CHj-CH-CH-COOH 



Threonine precursor 



30,000 



100,000 



PGA 



NHj 



HOCH2-CH-COOH 



Serine 



NH-C=0 



I I 

 0=C C-CH3 



I II 



NH-CH 



Thymine 

 (or derivative) 



Fig. 8. Inhibition analysis with sulfanilamide (E. coli). Courtesj^ Ann. N. Y 

 Acad. Sci. (Shive^). 



of the amine is prevented by addition of p-aminobenzoic acid in concentra- 

 tions sufficient to block the action of the sulfonamide. Other bacteriostatic 

 agents such as atebrin or penicillin do not produce this diazotizable amine. 

 Tlie fact that this amine forms under conditions of sulfanilamide inhibi- 

 tion where purine synthesis is inhibited, together with the fact that the 

 empirical analysis corresponded to that of a purine minus one carbon atom, 

 suggested that it might well be an intermediate in purine sjnithesis. On 

 this basis Shive et al.^^ synthesized 4-amino-5-imidazolecarboxamide and 



M. R. Stetten and C. L. Fox, Jr., ./. Biol. Chcm. 161, 333 (1945). 

 " W. Shive, W. W. Ackermann, M. Gordon, M. E. Getzendaner, and R. E. Eakin, 

 ./. Am. Chcm. Soc. 69, 725 (1947). 



