14 Carbon Assimilation. 



might combine with another carboxyl group.' 



From the formulee of chlorophyll given above it will be observed, 

 that the piiytol component amounts to one-third of the weight of 

 the chlorophyll. 



Now analysis of chlorophyll from different plants gave very 

 various numbers for the phytol content, and plants yielding 

 chlorophyll containing very little phytol were found to be excellent 

 material from which to isolate chlorophyll in a crystalline form. 

 According to Willstatter and StoU the chlorophyll in plants is 

 accompanied by an enzyme chlorophyllase, active in alcoholic media, 

 which brings about the replacement of the phytol of the chlorophyll 

 molecule by alcohol, so that one gets alcoholysis of the chlorophyll. 

 The substances so produced were known formerly as crystalline 

 chlorophyll. They constitute a group called chlorophyllides. Ethyl 

 chlorophyUide (crystalline chlorophyll) is produced according to the 

 equation 



(Cg^HgoON.Mg) (COOCH3) (COOC^oHss) + C,H,OH= 

 C,„H330H + (C3,H3oON,Mg) (COOCH3) (COOC.H,). 



Phytol. Ethyl chlorophyUide. 



Similar chlorophyllides are produced with other alcohols. 

 Of much interest is the manner in which the presence of two 

 chlorophylls in leaves was discovered. It has been mentioned 

 already that the treatment of an alcoholic extract of leaves with 

 dilute acid yields a wax-like substance called phseophytin. It was 

 observed by Willstatter that the decomposition of phseophytin 

 results in a considerable number of products, but that these consist 

 of two distinct groups, one called the phytochlorins which are olive- 

 green in solution, and another group, comprising those which give 

 solutions of a beautiful red colour, called phytorhodins. These 

 compounds were so numerous that they were simply differentiated 

 by letters so that they were designated phytochlorin a, phytochlorin 

 b, etc. 



The method by which they were separated by Willstatter and 

 Mieg (1906) is based on the different distributions of these substances 

 between ether and hydrochloric acid. The concentration of the 

 hydrochloric acid determines how much of the substance is extracted 

 by it from ether. Thus only traces of phseophytin a are extracted 



' In alcoholic solution chlorophyll undergoes a change which Willstatter 

 calls allomerisation. He supposes the lactam ring is opened and another 

 lactam ring formed. Such allomerised chlorophyll does not give the brown 

 phase. This change does not take place in ether or chloroform solutions. 

 It is accelerated in alkaline solutions but inhibited by small quantities of acid. 

 Therefore, in the separation of the two chlorophylls, a small quantity of 

 oxalic acid is added. See section D (6), p. 23. 



