STABILITY 



References to Section 5 



1. H. K. Mitchell and R. J. Williams, /. Amer. Chem. Soc, 1944, 66, 



271. 



2. H. K. Mitchell, ibid., 274. 



3. B. A. Hall Biochem. J., 1947, 41, 287. 



4. J. J. Pfiffner, S. B. Binkley, E. S. Bloom, R. A. Brown, O. D. 



Bird, A. D. Emmett, A. G. Hogan and B. L. O'Dell, Science, 

 1943. 97, 404. 



5. E. L. R. Stokstad, /. Biol. Chem., 1943, 149, 573. 



6. E. L. R. Stokstad, B. L. Hutchings and Y. SubbaRow, /. Amer. 



Chem. Soc, 1948, 70, 3. 



7. B. L. O'Dell, Univ. Microfilms Ann Arbor, 1944, 5, No. 2, 19. 



8. B. L. Hutchings, E. L. R. Stokstad, N. Bohonos and N. H. Slobod- 



kin, Science, 1944, 99, 371 ; B. L. Hutchings, E. L. R. Stokstad, 

 M. Bohonos, N. H. Sloane and Y. SubbaRow, /. Amer. Chem. 

 Soc, 1948, 70, I. 



9. J. J. Pfiffner, D. G. Calkins, B. L. O'Dell, E. S. Bloom, R. A. 



Brown, C. J. Campbell and O. D. Bird, Science, 1945, 102, 228. 



10. E. L. Rickes, L. Chaiet and J. C, Keresztesy, /. Amer. Chem. Soc, 



1947, 69, 2749. 



11. D. E. Wolf, R. C. Anderson, E. A. Kaczka, S. A. Harris, G. E. 



Arth, P. L. Southwick, R. Mozingo and K. Folkers, ibid., 2753. 



6. STABILITY OF FOLIC ACID 



Pteroylglutamic acid is labile to acid, 70 to 100 % of the activity 

 being destroyed on autoclaving at pH. i.^' ^ It becomes progressively 

 more stable as the pK increases and is relatively stable to heat within 

 the pm range 4 to 12. At plrL 6-8, for instance, solutions can be sterilised 

 by heating for thirty minutes without loss of potency. 



Folic acid is partially inactivated by lead and mercury salts ^ and 

 by treatment with sulphite. ^ Aeration at pK 10 also causes partial 

 inactivation.2 



In pure solutions, it is rapidly inactivated by light, ^' ^ with formation 

 of ^-aminobenzoylglutamic acid ^ and 2-amino-4-hydroxy-6-formyl- 

 pteridine ^<* ; the latter is converted first into the corresponding acid 

 and then into 2-amino-4-hydroxypteridine. 



Vitamin Be Conjugase 



Vitamin B© conjugate (pteroylheptaglutamic acid) is converted 

 into pteroylglutamic acid by the action of an enzyme, known as 

 vitamin Bo conjugase (page 460). This is present in pig kidney,* 

 the liver and small intestine of the pig,^» ®in ox liver,^' ^ chick pancreas,^* ^ 

 chick liver, '^ and almonds.* The enzjnne also converts pteroyltri- 

 glutamic acid into pteroylglutamic acid, Day et al. ® obtaining a 23-fold 



479 



