64 VITAMINS A AND CAHOTENES 



powder — about 0.6 g. to oxidize 10 mg. of vitamin A — into a piece of glass 

 tubing, so as to form a short column of the kind used in chromatography. 

 A solution of vitamin A in petroleum ether is poured in at the top and is 

 drawn through under light suction. An almost pure solution of retinene 

 runs off as the filtrate. ^^' '^ 



I have called this process a chroynatographic oxidation. It is an example 

 of what Tswett, the founder of chromatography, foresaw might become a 

 widespread class of reactions, in which a solid acts at once as adsorbent 

 and reagent. It seems probable that such processes display a degree of 

 specificity and molecular orientation to be found otherwise only in enzyme 

 systems. The force of this consideration will appear in connection with 

 another such reaction which is considered below. 



C. VITAMIN A2 AND RETINENE2 



The first correct characterization of vitamin A2, and the first — and still 

 the only — -demonstration that it is a vitamin, appeared in a biochemical 

 description of the visual systems of fresh- water fishes.'^ This paper also 

 first characterized retinene2 and described the part that both substances 

 play in the porphyropsin system. Both substances were identified through 

 the absorption bands which they yield in the reaction with antimony 

 chloride, vitamin A2 as the 696-m/i chromogen, retinene^ as the 703-m/i 

 chromogen. 



The term vitamin A2 was not used in this paper but was introduced shortly 

 afterward on the basis of these observations.^^ A few months earlier Lederer 

 and Rosanova^^ had described in the Russian journal Biokhimiya "an 

 abnormal reaction" in the antimony chloride test with liver oils of certain 

 fresh-water fishes. The "abnormality" consisted in the appearance of pre- 

 dominant absorption bands at 645 and 690 m/x. The authors assigned the 

 main importance to the 645-m/x chromogen: "further experiments will 

 show, whether really the chromogen 645 of fish liver oils can act as a vita- 

 min A." Some years earlier, Heilbron et alP had noted in antimony chloride 



i« Mr. P. K. Brown in our laboratory has found that the addition of about 2% abso- 

 lute ethyl alcohol to the vitamin A solution in petroleum ether results in a purer 

 product and an increased yield. Preparations of manganese dioxide, however, 

 vary considerably in activity. As with all adsorbents, the physical state of the 

 solid particles has much to do with their action. The directions given here, and 

 given below for the oxidation of vitamin A 2, hold for the most active preparations 

 that we have examined. With weaker preparations, larger amounts of manganese 

 dioxide are needed. 



" G. Wald, Nature 139, 1017 (1937). 



'8 E. Lederer, V. A. Rozanova, A. E. Gillam, and I. M. Heilbron, Nature 140,233 

 (1937); J. R. Edisbury, R. A. Morton, and G. W. Simpkins, Nature 140, 234 (1937). 



'9 E. A. Lederer and V. A. Rozanova, Biokhimij/a 2, 2 (1937). 



"o I. M. Heilbron, A. E. Gillam, and R. A. Morton, Bwchem. J. 25, 1352 (1931). 



