III. lUOCHEMICAL SYSTEMS 



65 



tests with marine fish Hver oils and concentrates the "appearance in certain 

 cases of bands at 635, 645, 656, 680 and 690 mM." It is sometimes said that 

 the presence of the number 600 in this Hst constitutes the discovery of vi- 

 tamin Aj; by the same token the remaining nimibers should mark the dis- 

 covery of vitamins A3 through Ae. 



The history of vitamin Ao in the years following its discovery was re- 

 markably confused. Very early it was reported to have growth-promoting 

 activity in rats;-* this was later denied,^- then reaffirmed.^'' 2* It is now 



CH3 CH3 



\ / 



C CH3 CH3 



/ \ I I 



H2C C— C=C— C=C— C=C— C=C— CH2OH 



H H H H H H 



HC C— CH3 



\ / 

 C 

 H 



CH3 CH 



\ / 

 C 



/ 

 H2C 



Vitamin Ao, C20H27OH 



CH, 



CH3 



C— C=C— C=C— C=C— C=C— C=0 

 H H H H H H H 



HC C— CH3 



\ / 

 C 

 H 



Retinene2, C20H26O 

 Fig. 15. Structural formulas of vitamin A2 and retinene2. 



clear that it has such activity, although no rigorous proof has yet been pre- 

 sented that in the rat it acts directly, rather than as a provitamin Ai. Its 

 ozonolysis was claimed to yield geronic acid,-* then acetone,-- then formalde- 

 hyde,-'* in each case indicating chemical structures, all of which have since 

 been abandoned. 



2' A. E. Gillam, I. M. TTcill.ron, W. E. Jones, and E. Lederer, Biochem. J. 32, 405 



(1938). 

 22 P. Karrer, A. Ge'x^cv, and E. Bretscher, Helv. Chim. Acta 24, 161E (1941). 

 "J. L. Jensen, E. M. Shantz, N. D. Embree, J. D. Cawley, and P. L. Harris, /. 



Biol. Chem. 149, 473 (1943). 

 " P. Karrer and E. Bretscher, Helv. Chim. Acta 26, 1758 (1943). 



