XIII. SULFONAlSnOE UKVKHSAL 69 



acitl,--' arf>;iniiie,^" histidine,"*" lysine,-'*- *" ^lulainic acid,'" asparlic acid,'"' 

 isoleucinc,'-'' tryploplian,'"' •''- and valine'-'' have been reported. 



Considcralile clarilication with respect to the activities of the above 

 apparently unrelated compounds in reversing the action of sulfonamides 

 has come about from the use of inkibilion ajialysis as developed by Shive 

 and co-workers.-'"' ■ "*^ Inhibition analijsis has been explained in detail a 

 number of times by Shive, and these references should be consulted for a 

 full appreciation of the possibilities inherent in the procedure as well as 

 the significance of the terms used to describe the results obtained. 



Sulfonamides inhibit the functioning of PABA in Escherichia coli as 

 determined by Shive and coworkers in a synthetic salts-glucose medium 

 with an inhibition index of about 3000 (1 part of PABA will reverse the 

 effect of 3000 parts of sulfanilamide).'^ In the presence of methionine, this 

 inhibition ratio is increased to 10,000 (which indicates that more sulfanil- 

 amide is required for inhibition in the presence of methionine). Thus it 

 would appear that one function of PABA, not necessarily as such but in a 

 form whose synthesis is inhibited by sulfanilamide, is concerned with 

 methionine sj'nthesis. The reaction affected is postulated by Shive and 

 coworkers as follows : 



NH2 . ^.^.^. NH2 



I inhibition i 



I index, 3000 ^ I 



HSCH2CH2CHCOOH CH3— S— CH2CH2CHCOOH 



Homocysteine (or related Methionine 



precursor) 



In the presence of methionine the inhibition index of sulfanilamide for 

 Escherichia coli may be raised from 10,000 to about 30,000 by purines.'* 

 Purines and their related compounds effective in reversing sulfanilamide 

 under these conditions include adenosine, xanthine, guanine, and inosine. 

 Adenine not only is ineffective in reversing sulfanilamide but acts syn- 

 ergistically as an inhibitor. 



An increase in the inhibition index from 10,000 to 30,000 with addition 

 of purines to the medium indicates that PABA functions in the synthesis 

 of purines. In this case the precursor of the reaction blocked by the failure 

 of PABA, in the presence of sulfanilamide, to be converted to a meta- 

 bohcally active form has been elucidated. There accumulate in Escherichia 



30 F. Nitti, J. Tabone, and H. Mousset, Ann. inst. Pasteur 70, 366.. 379 (1944). 



31 M. G. Sevag and M. X. Green, ./. Bactcriol. 48, 623 (1944). 



32 M. G. Sevag and M. N. Green, ./. Bacterial. 48, 631 (1944). 



" W. Shive, Ann. N. Y. Acad. Set. 52, 1212 (1950); M. Gordon, Ph.D. Thesis, Uni- 

 versity of Texas, 1948. 



3^ R. J. Williams, II. E. Eakin, E. Beerstecher, Jr., and W. Shive, The Biochemistry 

 of B Vitamins, p. 458. Reinhold Publishing Corp., New York, 1950. 



3^ W. Shive and E. C. Roberts, J. Biol. Chetn. 162, 463 (1946). 



