190 Aljred J. Eivart: 



The C071 version of xanthophi/ll into carotin. 



Haas'i and Hill state apparently on the authority of Palladin2 

 that carotin is converted by a plant oxidase into xanthophyll, and 

 xanthophyll by a reductase into carotin. The same statement is 

 definitely referred to Palladin by C. J. West, 3 but is evidently tran- 

 scribed from Haas and Hill. As a matter of fact Palladin does not 

 mention either carotin or xanthophyll in the papers quoted. He 

 shows that reductases are present in plants as well as oxidases. 

 The respiratory oxidases, he considers to be pigment forming 

 oxidases, and (on p. 385) "at present we only know that the respi- 

 ratory chromogens are aromatic compounds; while in the living 

 plant the respiratory pigments usually occur as colourless chromo- 

 gens, and when present in coloured form (l:>eet root, etc.) can be 

 reduced to colourless compounds."* 



In my previous paper^ I was also misled into ascribing this state- 

 ment to Palladin, but could obtain no evidence of any action of 

 either watery or glycerine extracts of plants oxidases and reductases 

 on carotin or xanthophyll. This may possibly be because of the 

 difficulty of reproducing the conditions existing in the plant. 

 Experiments were, however, made with the pigments in various 

 solvents, and in the form of fine emulsions in water. 



The results obtained with metallic reductases were more satis- 

 factory. As already shown, magnesium dust rapidly, and zinc 

 ■dust slowly, reduce xanthophyll, present in a clear yellow solution 

 in a mixture of alcohol and water, to carotin, leaving the liquid 

 nearly colourless. Using strong emulsions of xanthophyll in the 

 form of suspended particles, zinc dust was found to be ineffective 

 and magnesium dust only acted slowly. In the latter case on filter- 

 ing, drying and dissolving, the dry residue in petrol ether, the 

 bulk of the pigment consisted on evaporating of yellow xantho- 

 phylloids with scattered minute red particles of carotin. The tests 

 should be done in darkness, and as far as possible out of contact 

 with the air since otherwise the carotin may oxidize to colourless 

 products. 



All attempts to convert carotin into xanthophyll by the aid of 

 metallic oxidases, organic oxidases (carrot, potato, apple) or direct 



1 Chemistry of Plant Products, p. 252. 



2 Ber. d. D. Bot. Ges. 1908, 26, A, pp. 12.i, 378, 398; (1909), 27, p. lid. Zeitschr. f. Physiol. 

 Chemie. (190S). 55, p. 207. 



3 Biochemical Bulletin, 1915, p. 184. 



4 Zeit.s. t. Physiol. Chem., B^. sr., 1008, p. 221. 

 r- Pi-oc. Roy. Soc, B, 89, W\f>, p. 11. 



