THE FOLIC ACID COMPLEX 



together with a crude source of the extrinsic factor (page 498) from 

 which pteroylglutamic acid had been eliminated. 



The antibacterial index of 7-methylfolic acid was approximately 

 30 for L. helveticus in the absence of purines and pyrimidines.^'^ The 

 addition to the medium of adenine, guanine, hypoxanthine or xanthine 

 increased the antibacterial index to about 100. Thymine alone had 

 no effect but, in the presence of purines, the antibacterial index was 

 increased to over 1000. This evidence appears to give further support 

 to the theory of J. L. Stokes ^ that folic acid is concerned in the biosyn- 

 thesis of thymine. 



The inhibitory action of methylfolic acid for L. helveticus was 

 antagonised by liver extracts to an extent 15 times greater than could 

 be accounted for by their folic acid contents. A concentrate was 

 prepared from hog liver that was somewhat more active than folic 

 acid in antagonising the effect of methylfolic acid on L. helveticus and 

 10 to 100 times as effective with S. faecalis R. The new factor has 

 been named folinic acid and proved to be as effective a growth factor for 

 these two organisms as is folic acid. It also stimulated the growth of 

 Leuconostoc citrovorum, an organism on which folic acid has no effect ; 

 on mild acid hydrolysis folinic acid was apparently converted into 

 folic acid.^"^" 



9-MethylfoHc Acid, N*»-Methylfolic Acid and 9 : N*®-Dimethyl- 

 folic Acid 



9-Methylfolic acid also antagonises folic acid, but is much less potent 

 than 7-methylfolic acid, having an antagonist activity of only o-i 

 with S. faecalis R.^'^ N^'^-Methylpteroylglutamic acid was much 

 more potent, with an antagonist activity of 100 against S. faecalis 

 R, but N^o-phenacylpteroylglutamic acid was much less active. 

 9 : N^^-Dimethylpteroylglutamic acid had an antagonist activity of 

 3.4.27a 



Pteroylaspartic Acid 



A homologue of a rather different type, which likewise had 

 anti-folic acid properties was pteroylaspartic acid.^^ This has one 

 methylene group less in the amino acid radicle than has folic 

 acid, and it was shown to be antagonistic to folic acid both with 

 L. helveticus and with the chick. With S. faecalis R, the inhib- 

 itor prevented the utilisation of pteroic acid, pteroylglutamic acid, 

 pteroyl-y-glutamylglutamic acid and pteroyl-y-glutamyl-y-glutamyl- 

 glutamic acid. In all instances, the inhibition was competitive in 

 nature. 



520 



