KARL FOLKERS 



yeast and liver extracts contained an excess of the pyridoxamine frac- 

 tion, and animal assays showed no marked difference in the activity 

 of the three substances. By assuming that the yeast supply used by 

 Kuhn and Wendt and by Gyorgy contained an excess of pyridoxamine 

 also, it is evident that at one or more of the steps in the isolation proc- 

 ess the pyridoxamine was lost. Williams (65), in commenting on 

 Gyorgy's communication (11) on isolation, noted that the yield of 

 active substance in the first few steps of the concentration was only 

 10 to 30% of the original activity. If the isolation of vitamin Be 

 from yeast had been guided by the results of microbiological assays with 

 .S*. Jaecalis R instead of rats, one might predict today that it is quite 

 probable that pyridoxamine would have been isolated instead of pyri- 

 doxine and the pyridoxine present would have been lost at some step 

 of the isolation procedure. 



In the field of new vitamins of unknown structure, several sub- 

 stances are currently of great interest and papers concerning them 

 are appearing frequently in the literature. Although studies of bio- 

 logical activities in animals are being made, the use of microorganisms 

 for tests of biological activities is resulting in the rapid accumulation 

 of much valuable data on the differentiation of these substances. The 

 following citations may exemplify the importance of the role of micro- 

 organisms in the study of these new growth factors. 



Snell and Peterson (52) and Hutchings, Bohonos, and Peterson 

 (19) have described the preparation and some properties of a con- 

 centrate of a norite eluate factor from liver and yeast which resulted 

 from a study of the nutrient requirements of L. casei and related lactic 

 acid bacteria. Mitchell, Snell, and Williams (33) reported on the 

 preparation of a highly purified nutrilite from spinach which they 

 designated folic acid and defined as the material responsible for the 

 growth stimulation of S. lactis R. Crystalline vitamin Bg from liver 

 was highly active in growth activity for L. casei according to Pfiffner, 

 Binkley, Bloom, Brown, Bird, Emmett, Hogan, and O'Dell (39). 

 Stokstad (56) has described some properties of two crystalline prepara- 

 tions, one from liver and one from yeast, which had somewhat different 

 activities for promoting the growth of L. casei and S. lactis R. Keresz- 

 tesy, Rickes, and Stokes (24) have reported the isolation of a different 

 factor which was highly active for the growth of S. lactis R but rela- 

 tively inactive for the growth of L. casei. Another new compound 



lOO 



