VITAMIN L AND FACTORS U, W, R AND S 



cell proliferation and haemopoiesis was enhanced by certain enzyme 

 preparations, such as xanthine oxidase from milk, rat liver homogenate 

 and rat gastric mucosa extract, the activity of vitamin B^^ was not 

 affected. The enzyme- treated pterines had about the same activity 

 as vitamin B^^. 



References to Section 4 



1. G. M. Briggs, T. D. Luckey, C. A. Elvehjem and E. B. Hart. / 



Biol. Chem., 1943, 148, 163. 



2. R. C. Mills, G. M. Briggs, T. D. Luckey and C. A. Elvehjem, Proc 



Soc. Exp. Biol. Med., 1944, 56, 240. 



3. J. McGinnis, L. C. Norris and G. F. Heuser, /. Biol. Chem., 1942 



145. 341- 



4. C. A. Nichol, L. S. Dietrich, C. A. Elvehjem and E. B. Hart, / 



Nutrition, 1949, 39, 287. 



5. A. F. Novak and S. M. Hauge, /. Biol. Chem., 1948, 174, 235, 647 



6. E. R. Norris and J. J. Majnarich, Science, 1949, 109, 32, 33. 



5. VITAMIN L AND FACTORS U, W, R AND S 

 Vitamin L 



Vitamin L is the name given by Nakahara et al.^ to a factor said 

 to be essential for the lactation of rats. Its name represents a return 

 to the original system of naming the vitamins, in which successive 

 letters of the alphabet are used. Its " discovery " occurred shortly 

 after that of the fat-soluble anti-haemorrhagic vitamin K, and was 

 followed in turn by the discovery of vitamin M which, as already 

 observed, is now regarded as a conjugate of folic acid. 



Nakahara et al.^ subsequently claimed to have separated vitamin 

 L into two fractions, vitamin L^ and vitamin Lg, neither of which 

 could replace the other. Unfortunately, although these factors were 

 claimed to be distinct from the filtrate factor and factor W, they 

 appear not to have been isolated in the pure state, and so their rela- 

 tionship to other members of the vitamin B complex cannot be deter- 

 mined. Folley et al.^ failed to confirm the existence of a lactation 

 factor for rats. 



Factor U 



Another factor of doubtful status is the factor U of E. L. R. 

 Stokstad and P. D. V. Manning.^ This was said to be required by 

 chicks on a diet of polished rice and washed fish meal, supplemented 

 by riboflavine and the chick antidermatitis factor. In a later paper,^ 

 a factor U concentrate was shown to contain vitamin Bg, which 

 would have accounted for some of its activity. 



615 



