CHEMISTRY OF CHLOROPHYLL: THE CAROTINOIDS 51 



The Carotinoids — Associated with the chlorophyll in the leaf 

 are two other pigments, which are extracted by ethyl alcohol 

 at the same time as the chlorophyll and later must be separated 

 from it if pure chlorophyll is desired. The most important of 

 these is carotin which receives its name from its color (Gr., reddish- 

 yellow) and its abundance in carrots. The color of yellow and 

 orange petals is commonly due to this pigment. It is also abundant 

 in yellow tomatoes and in seeds such as yellow corn. 



Carotin is very soluble in carbon disulphide, from which it may 

 be precipitated as orange crystals, which are orange-red by trans- 

 mitted light and greenish-blue by reflected light. Willstatter has 

 determined the formula as C 4 oH 56 . Lycopin, isolated from red 

 tomatoes and red peppers, is an isomer. If tomatoes which are 

 normally red are ripened at temperatures above 30° C. they will 

 be yellow instead of red, showing the presence of the isomer, 



carotin. 



Closely associated with carotin and related to it is xanthophyll, 

 C4oH 56 02. This seems to be an oxide of carotin, but it has not yet 

 been possible to oxidize carotin to xanthophyll in the laboratory. 

 This does not preclude the possibility, however, that the two sub- 

 stances may be transformed into each other in the plant. Such 

 transformations might then be analogous to the changes from 

 hemoglobin to oxyhemoglobin, and the reverse, in the blood of 

 animals during respiration. 



Xanthophyll is more yellow than carotin, is much less soluble 

 in carbon disulphide, and more soluble in acetone; and, as the two 

 chlorophylls are separated from each other on the basis of their 

 differential solubilities in various solvents, in like manner the 

 carotinoids may be separated from each other and from the 



chlorophylls. 



From the brown algse Willstatter has isolated a pigment called 

 fucoxanthin with the formula C 4 oH 5 40 6 which indicates its relation 

 to the other carotinoids. It is brownish-red with basic properties. 



The carotinoids, unlike chlorophyll, will form in darkness and 

 seem to undergo very little change or decomposition in the digestive 

 tract of animals. The yellow yolk of eggs contains carotinoids, 

 and if chickens are fed on white corn instead of yellow and kept 

 from getting green foods, the yolks soon become pale and color- 

 less. Similarly the yellow color of the feathers and of the leg 

 scales is connected with an abundant carotinoid diet. 



