200 PTEROYLGLUTAMIC ACID 



glutamic acid were reported by Kidder^^^ to be approximately as active as 

 PGA when compared on a molar basis. Thus the ability of this ciliated 

 protozoan to utilize PGA conjugates and its inability to use pteroic acid 

 and rhizopterin parallels that of the rat, the chick, and the human. 



Clostridium ietani was early reported by Mueller and Miller^^"' ^^^ to re- 

 quire an unknown growth factor which could be replaced by concentrates 

 of PGA prepared from liver or by folic acid preparations obtained from 

 spinach. 



1. Metabolism of Rhizopterin 



A survey of the rhizopterin and PGA requirements of a number of lactic 

 acid bacteria was made by Stokes et al}'^^ This showed that all Streptococci 

 which were stimulated by rhizopterin (N^^-formylpteroic acid) also re- 

 sponded to PGA. A certain number of organisms, including both Lacto- 

 bacilli and Streptococci, responded only to PGA, and a third group responded 

 to neither. They also found that different strains of the same organism 

 vary widely in their requirements. Thus one strain of S. faecalis can use 

 either rhizopterin or PGA, another responds to PGA only, and a third 

 requires neither. The strains that do not require PGA were found to syn- 

 thesize this factor when grown on a medium devoid of the vitamin. 



An interesting observation made by these same investigators was the 

 finding that certain Enterococci are able to convert rhizopterin into a form 

 active for L. casei. Presumably this conversion involves the addition of 

 glutamic acid to rhizopterin to give either PGA or N'^-formylpteroylglu- 

 tamic acid. Resting cell suspensions are also able to effect this conversion."'' 

 A 10-ml. resting cell suspension of S. lactis R or S. zymogenes converts 5 y 

 of rhizopterin to about 1 7 of PGA"^ in 3 hours. Two other strains formed 

 only 0.18 7 under similar conditions which shows the wide variation in the 

 ability of various organisms to effect this conversion. The conversion rate 

 is increased by the addition of carbohydrates which were able to act as 

 hydrogen acceptors as evidenced by reduction of methylene blue. 



Some interesting facts regarding the assay of PGA in microbial cells were 

 revealed in this same study. "^ In the assay of PGA formed from conversion 

 of rhizopterin by resting cells, the entire cell suspensions were added di- 

 rectly to the assay medium without any preliminary treatment. The bulk 

 of the activity was found to reside in the cell. When the cells were auto- 



"' G. W. Kidder, Paper presented at the New York Academy of Science, Dec. 7, 



1946. 

 "0 J. H. Mueller, P. A. Miller, ./. Biol. Chem. 140, 933 (1941). 

 '« J. H. Mueller, P. A. Miller, Froc. Soc. Expfl. Biol. Med. 49, 211 (1942). 

 i'2 J. L. Stokes, J. C. Keresztesy, and J. W. Foster, Science 100, 522 (1944). 

 1" J. L. Stokes and A. Larsen, ./. Bacteriol. 50, 219 (1945). 

 '^^ The data have been recalculated on the basis of PGA's liaAnns the same activity 



as folic acid of potency 137,000. 



