VITAMINS 



247 



in addition to previously known vitamins, for the normal growth of these 

 organisms. The effective substance present in such preparations was 

 later found to be identical with "factor U" and "vitamin M," which at 

 that time were still unidentified, but were recognized as dietary essentials 

 for chicks and monkeys, respectively. Other investigators, working with 

 various experimental animals, proposed still other names for vitamin- 

 like substances which eventually turned out to be pteroylglutamic acid, 

 or closely related compounds. These names included "vitamin Be," 

 "factor R," "factor S," "folic acid," "S. lactis R factor or SLR factor," 

 "liver L. casei factor." The term folic acid is still in use, but should 

 now be replaced by the proper chemical names (see below). 



Chemical nature 



Pteroylglutamic acid is a complex substance made up of three parts, 

 glutamic acid, para-aminobenzoic acid (p. 254), and a pterin, chemically 

 linked together: 



H 



_N N C 



H2N— C^')"^C^'^*)^CH HC^^^'^'^C-CONHCHCHiCHiCOOH 



1(2) II (^) I II (5') (l')| I 



N5^)i^(^)Sc-CH.NH-ci:;;3')|^tH COOH 



I H 



OH 



Pteroylglutamic acid 



This substance is identical with the "liver L. casei factor," vitamin Be, 

 and folic acid. The name folacin was proposed in 1949 by the American 

 Institute of Nutrition as a synonym for folic acid. The "fermentation 

 L. casei factor" is very similarly constituted except that three glutamic 

 acid residues are present. In this form, also called teropterin, the second 

 and third glutamic acid residues are linked to the preceding one through 

 the gamma carboxyl group rather than through the alpha carboxyl (see 

 p. 131). This is the same type of peptide linkage as is found in gluta- 

 thione. Still another form, vitamin Be conjugate, contains seven glutamic 

 acid residues. The SLR factor, or rhizopterin, contains no glutamic acid 

 at all but bears an aldehyde or formyl group on the nitrogen atom in 

 position 10: 



H,N-G^(^^C-^S^CH CHO C-C 



1(3) II el I / W 



n4:(4) ^C^ (5)!^^C-CH,-N-C c-cooh 



C N (9) (10) \ / 



I HC=CH 



OH 

 Formylpteroic acid (or rhizopterin) 



