8 PHYSIOLOGY OF NUTRITION 



Almost a third of the chlorophyll molecule is composed of phytyl, the radical 

 of phytol, 1 an unsaturated mono-hydric primary alcohol of the aliphatic series, 

 having the composition C 2 oH 40 and the probable structure shown by the 

 following diagram: 



СНз— CH— CH— CH— CH— CH— CH— C=C CH— CHoOH 



I I I I I I I I I 



CH3 СНз СНз СНз СНз СНз СН3СН3 СНз 



Phytol is readily oxidized in the presence of air. Willstätter suggests that it 

 may be obtained from isoprene in the following way: 



4С5Ш (isoprene) + H 2 -f зН 2 = C 20 H 4 oO (phytol). 



Carotin appears also to be related to isoprene. The phytyl of chlorophyll 

 may be replaced by the ethyl group if the leaves are treated with ethyl alcohol. 

 This replacement is effected by an enzyme known as chlorophyllase. 2 



Another alcohol radical is present in both the chlorophylls, namely, methyl 

 (CH3). They thus appear to be esters of a complex, dicarboxylic acid, one of 

 the two carboxyls (COOH) being joined to phytyl and the other to methyl. 



Regarding the complex acids that form the basis of the chlorophylls, there still 

 remain some uncertainties, but it appears to be related to a tricarboxylic acid 

 that may be represented by the formula (C 3 iH 29 N 4 Mg) (COOHh, but one of the 

 carboxyls is inactive, so that a dicarboxylic acid results. A general idea öf the 

 manner in which the magnesium atom is probably related to the other compo- 

 nents of the molecule may be obtained from the following structural formula 

 for etiophyllin, to which this fundamental acid is apparently closely related. 



When the phytyl group of chlorophyll a is replaced by the ethyl group 

 (C2H5), a substance is obtained (CsyHssOe^Mg) which Willstätter called 

 ethyl chlorophyllide. This forms beautiful crystals, which were earlier mistaken 

 for pure chlorophyll. Chlorophyll b reacts in a similar way. According to the 



1 Willstätter, Richard, and Hocheder, Ferdinand, Ueber die Einwirkung von Säuren und Alkalien auf 

 Chlorophyll. Liebig's Ann. Chem. u. Pharm. 354: 205-258. 1907. Willstätter, Richard, Mayer, Erwin 

 W., and Huni, Ernst, Ueber Phytol. I. Ibid. 378: 73-152. 1911. 



2 Willstätter, Richard, and Stoll, Arthur, Ueber Chlorophyllase. Liebig's Ann. Chem. u. Pharm. 

 378: 18-72. 1911. 



