VI. ESTIMATION 161 



ct a?.'"^). This strain was also resistant to other 4-amino PGA derivatives 

 but was not resistant to 2,G-diaminopurine or to "x methyl PCIA" with a 

 PGA-deficient diet containing a sulfonamide.'"^ This therapeutic effect of 

 "x methyl PGA" on a strain of transplanted mouse leukemia in Ak mice 

 had previously been demonstrated by Weir et al.^°^ An interesting metabolic 

 difference between the normal strain, Ak4, and the resistant strain, Ak4R, 

 lies in their relative ability to incorporate radioactive formate into the 

 nucleic acid purines. Both strains have the same ability in this respect in 

 the absence of antagonist. On the administration of 4-amino- 10-methyl 

 PGA the incorporation of radioactive formate was reduced to 4 % of its 

 original level in the normal Ak4 strain but was reduced to onty 25 % in the 

 resistant Ak4R strain (Skipper and Burchenal""). 



Pteroyltriglutamic acid has been reported by Leuchtenberger, Lewisohn, 

 and associates'^' • "- to produce complete regressions in spontaneous breast 

 tumors in mice. Intravenous injection of 5 7 per day led to complete re- 

 gressions in 43% of a group of eightj^-nine animals. No regressions occurred 

 in sixty control animals. In contrast, PGA had no inhibitory effect, and it 

 was observed that primary tumors in mice receiving 100 7 of PGA grew 

 more rapidly than the untreated controls. The effect of pteroyltriglutamic 

 acid on transplanted sarcoma 180 has not been confirmed in investigations 

 bv Rurchenal et al.^^ and Schoenbach et al}^^ 



VI. Estimation 



E. L. R. STOKSTAD 



A. CHEMICAL METHODS 



Pteroylglutamic acid on reduction in acid solution is split to yield a 

 methj'lpteridine and p-aminobenzojdglutamic acid.' This reaction has been 

 made the basis of a ciuantitative procedure- in which the sample is reduced 



'"* J. Burcheiical, S. F. .John.ston, and G. B. Waring, Froc. Soc. Exptl. Biol. Med. 78, 



.348 (1951). 

 "" D. R. Weir, A. D. Welch, and R. W. Heinle, Proc. Soc. Exptl. Biol. Med. 71, 107 



(1949). 

 "» H. E. Skipper and J. H. Hurchenal, Cancer Research 11, 229 (1951). 

 '" R. Lewisohn, C. Leuchtenberger, and J. C. Keresztesy, Scieiu-e 104, 436 (1946). 

 "- H. Leuchtenberger, C Leuchtenberger, I). Laszlo, and R. Lewisohn, Science 101, 



46 (1945). 

 "3 E. B. Schoenbach, A. Goldin, B. Goldberg, and L. G. Ortega, Cancer 2, 57 (1949). 

 ' B. L. Hatchings, E. L. R. Stokstad, J. H. Mowat, J. H. Boothc, C. W. Waller, 



R. B. Angier, J. Semb, and Y. SubbaRow, ./. Am. Chem. Soc. 70, 10 (1948). 

 2 B. L. Hutchings, E. L. R. Stokstad, .J. U. Boothe, J. H. Mowat, C. W. Waller, 



R. B. Angier, J. Semb, and Y. SubbaRow, ./. Biol. Chem. 168, 705 (1947). 



