VII] 



OXIDIZING ENZYMES 



105 



Quercetin 



All the anthocyan pigments so far isolated, however, have been 

 found to contain the flavonol, and not the flavone, nucleus. 



Just as in the case of the flavone and flavonol pigments, some of 

 the anthocyan pigments are specific, while others, on the contrary, are 

 common to various genera and species. Also more than one anthocyan 

 pigment may be present in the same plant. 



It will be pointed out later that small amounts of a substance iden- 

 tical with cyanidin are said to be formed by reduction of quercetin with 

 nascent hydrogen, but this does not necessarily prove that the formation 

 of anthocyan pigments in the plant takes place on the same lines. If 

 we compare the formulae for a number of anthocyan with flavone and 

 flavonol pigments, it is seen that they may be respectively arranged in 

 a series, each member of which differs from the next by the addition of 

 an atom of oxygen : 



Luteolin, kaempferol and fisetin C 15 H 10 O 6 

 Quercetin C 15 H 10 O 7 

 Myricetin C 15 H 10 O 8 



Pelargonidin C 15 H 10 O 5 

 Cyanidin C 15 H 10 6 

 Delphinidin C 15 H 10 O 7 



The relationship between these two classes of substances in the 

 plant can only be ascertained by discovering which flavone, flavonol and 

 anthocyan pigments are present together, and then to determine whether 

 the relationship is one of oxidation or reduction, a problem which has 

 not yet received adequate attention (Everest, 6). 



A reaction which is of interest in connexion with the relationship 

 between the above two classes of pigments is that which takes place 

 when solutions of some flavone or flavonol pigments are treated with 

 nascent hydrogen. If an acid alcoholic solution of quercetin is treated 

 with zinc dust, magnesium ribbon or sodium amalgam, a brilliant magenta 

 or crimson solution is produced, and this solution gives a green colour 

 with alkalies (Combes, 5). The red substance thus produced has been 

 termed " artificial anthocyanin " or allocyanidin. The product is not a 



