THE FOLIC ACID COMPLEX 



that thymine can replace folic acid in the nutrition of certain micro- 

 organisms, but also by the observation that thymine reversed the 

 antagonistic effect of some uracil derivatives on folic acid ^ and, in 

 the presence of purine, increased many-fold the antibacterial index of 

 " methylfolic acid " for L. helveticus}^ 



A partial deficiency of pteroylglutamic acid lowered the desoxy- 

 ribonucleic acid content of L. helveticus, without affecting the ribo- 

 nucleic acid, whereas a deficiency of riboflavine or biotin or an excess 

 of thymine increased both.^^" 



It has also been suggested ^^ that pteroylglutamic acid is involved 

 in the synthesis of the porphyrin portions of metalporphyrin enzymes, 

 since pteroylglutamic acid partially reversed the inhibitory action of 

 cyanide, caffeine and hydrogen peroxide on 5. faecalis. 



Pteroylglutamic acid strongly inhibited the activity of xanthine 

 oxidase and of a xanthopterine oxidase prepared from either milk or 

 liver. 12 pteroic acid also inhibited the latter enzyme, but pteroyldi- 

 and tri-glutamic acid had no effect. Milk contained an enzyme that 

 transformed pteroylglutamic acid into a substance that had no in- 

 hibitory action on xanthopterine oxidase.^^ 



6-Pteridylaldehyde, obtained by the hydrolysis of pteroylglutamic 

 acid in sulphurous acid, was found to be 200 to 400 times as active 

 as folic acid in inhibiting xanthine oxidase, and also more active than 

 folic acid in inhibiting xanthopterine oxidase.^* It also inhibited 

 quinine oxidase. 



Thus folic acid and related compounds are capable of affecting a 

 number of different enzyme systems, and it remains to be seen which 

 of these are of physiological significance. 



References to Section 19 



1. J. E. Davis, Science, 1946, 104, 37 ; Amer. J. Physiol., 1946, 147, 



404. 

 la. R. D. Hawkins, Arch. Biochem., 1948, 17, 97. 

 lb. J. S. Dinning, C. K. Keith and P. L. Day, ibid., 1949, 24, 463. 



2. B. L. O'Dell, J. M. Vandenbelt, E. S. Bloom and J. J. Pfiffner, 



/. Amer. Chem. Soc, 1947, 69, 250. 



3. G. Rodney, M. E. Swendseid and A. L. Swanson, /. Biol. Chem., 



1947. 168, 395 ; 1949, 179, 19. 



4. M. E. Swendseid, I. F. Burton and F. H. Bethell, Proc. Soc. Exp. 



Biol. Med., 1943, 52, 202. 



5. C. W. Woodruff and W. J. Darby, /. Biol. Chem., 1948, 172, 851 ; 



C. W. Woodruff, M. E. Charrington, A. K. Stockell and W. J. 

 Darby, ibid., 1949, 178, 861. 

 ^a. C. D. Govan and H. H. Gordon, Science, 1949, 109, 332. 



6. G. J. Martin and J. M. Beiler, Arch. Biochem., 1947, 15, 201. 



7. G. J. Martin, L. Tolman and R. Brendel, ibid., 323. 



528 



