METABOLISM OF CAROTENOIDS AND VITAMINS A 549 



lieved to be presumptive evidence that stereoisomeric forms of vitamin A 

 other than all-^raws vitamin A and neovitamin A function in the animal 

 organism. 



c. Other Compounds Active as Sources of Vitamin A. (a) Vitamin A 

 Acid. The synthesis of this compound, in which the primary alcohol 

 group of vitamin A has been oxidized to a carboxyl group, was claimed by 

 Heilbron and co-workers^^^ in 1936, although these findings have been ques- 

 tioned.''^^ Its biologic potency is in the same range as that of vitamin A. 

 It required 4 /zg. to exert the same potency as 1 I.U. of vitamin A when the 

 acid was given in peanut oil. However Milas^*-* reported that its biopo- 

 tency was greatly increased when it was injected subcutaneously in aque- 

 ous solution as the sodium salt; 0.6 jug. of the vitamin A acid was equiva- 

 lent to one I.U. under these conditions. Bharucha and Weedon^^^ pre- 

 pared o-tolyl and mesityl analogues of vitamin A acid; the latter com- 

 pound had a slight vitamin A-like action, while the former derivative was 

 found to be inactive. A 4-carboxy derivative of vitamin A acid has been 

 found to have a slight biopotenc3^^°° Other data on \'itamin A acid are 

 contained in the papers of Arens and van Dorp,*"^ Karrer et al.,^'^^ and Heil- 

 bron and associates.^^'^°* 



(b) Vitamin A Aldehydes. Several of the vitamin A aldehydes are 

 natural products usually readily convertible to vitamin A. The al\-trans 

 form was first isolated from retinas by Wald^"^ in 1935; Morton,^"^ nine 

 years later, suggested that retinene is vitamin A aldehyde, which assump- 

 tion he later confirmed. ^''^ It was soon recognized that retinenei was 

 similar to vitamin Ai aldehyde, while a second type of retinene (retmene2) 

 was vitamin A2 aldehyde. -2^'°2^'*''*~^^'' Glover and co-workers'^^ were able 

 to demonstrate that vitamin A aldehyde is rapidly converted to vitamin A 



"8 1. M. Heilbron, W. E. Jones, A. Lowe, and H. R. Wright, /. Chem. Soc, 1936, 

 561-563. 



"^ K. R. Bharucha and B. C. L. Weedon, /. Chem. Soc, 1953, 1571-1577. 



^ B. M. Manly, V. Petrow, O. Stephenson, and S. W. F. Underhill, J. Pharm. and 

 Pharmacol., 4, 43-45 (1952). 



80' J. F. Arens and D. A. van Dorp, Nature, 157, 190-191 (1946). 



802 p. Karrer, E. Jucker, and E. Schick, Helv. Chim. Ada, 29, 704-711 (1946). 



803 1. ]\l. Heilbron, E. R. H. Jones, and D. G. O'SulUvan, Nature, 157, 485-486 (1946). 



80* I. M. Heilbron, E. R. H. Jones, and D. G. O'SulUvan, /. Chem. Soc, 1946, 866- 

 869. 



805 G. Wald, /. Gen. Physiol., 19, 351-371, 781-795 (1935-1936). 



806 R. A. Morton, Nat^ire, 153, 69-71 (1944). 



80^ R. A. Morton, M. K. Salah, and A. L. Stubbs, Biochem. J., 4I, xxiv (1947). 



808 R. A. Morton, M. K. Salah, and A. L. Stubbs, Nattire, 159, 744 (1947). 



809 H. R. Cama, P. D. Dalvi, R. A. Morton, M. K. Salah, G. R. Steinberg, and A. L. 

 Stubbs, Biochem. J., 52, 535-540 (1952). 



8'o R. A. iMorton, M. K. Salah, and A. L. Stubbs, Biochem. J., 40, lix-lx (1946). 



