382 



CARBOHYDRATE IVIETABOLISM 



The Anthocyanins. — Most of the red, blue, and purple pigments of 

 plants belong to the group known as the anthocyanins. These compounds 

 are glycosides which have been formed by condensation of a sugar (usually 

 glucose) with one of the compounds belonging to a group known as the 

 anthocyanidins. The anthocyanidins are derivatives of the compound flavone 

 which has the following structural formula: 



H 

 I 

 C 



HC C C- 



H 



I 



C: 



HC 



\ 



vv 



c c 



C-H 



C- 



I 

 H 



I 

 \ 



■ I 



./ 



I 

 H 



C— H 



H 



O 



Most of the anthocj^anidins are derived from flavone by reduction of the 

 oxygen atom of the middle ring, substitution of one or more hydroxyl groups 

 and addition of a chlorine atom by the reduced oxygen. 



The chemical formula of chrysanthemin chloride, a representative antho- 

 cyanin which occurs in species of the genus Chrysa7ithemu?n, illustrates the 

 molecular structure of these compounds : 



H 



I 

 C 



CI 



I 







H 



I 



c 



OH 



I 



c. 



HO 



—C C C C ( 



\. 



y 



C— OH 



H-C 



C-0-C6Hn05 H 



H 



I I 



OH H 



A number of chemically different anthocyanins have been isolated from 

 seed plants in which they are of widespread occurrence. They are also 

 found in some species of the lower plant groups. The anthocyanins are 

 water soluble, and when present in the cells are usually dissolved in the cell 

 sap, the cytoplasmic membranes being impermeable to them. Less commonly 

 these pigments are found in plant cells in the form of crystals or amorphous 

 solid bodies. Practically all anthocyanins are red in acid solutions and many 



