56o PRINCIPLES OF GENERAL PHYSIOLOGY 



On saponification by alkali, phseophytin shows itself to be an ester, the acid 

 contains nitrogen and has thirty-four carbon atoms, while the alcohol (called 

 "phytol") is free from nitrogen and is a monatomic alcohol of the composition 



C 20 H 40 O> 



Phytol appears to contain a number of groups CH in a chain. It is 



CH 3 



colourless, and of less interest than the coloured acid component. 



Chlorophyll is, therefore, a phytol-ester of a nitrogenous acid chlorophyllin, 

 which contains magnesium in organic combination. The acid of the phaeophytin 

 from chlorophyll a is olive-green in neutral solvents, and called phytochlorin. 

 That from chlorophyll 6 is red in neutral solution, and called phytorhodin. Since 

 it is an ester, it is not surprising to find that chlorophyll is accompanied in the 

 leaf by an enzyme (a lipase or esterase), which is active in alcoholic solution. In 

 extracting leaves with alcohol, " alcoholysis " of the chlorophyll takes place, and 

 ethyl takes the place of phytyl, forming an ethyl-chlorophyllide. The enzyme 

 acts synthetically, as would be expected, and forms chlorophyll in a concentrated 

 solution of phytol and the chlorophyll acid. The mono-carboxylic acid, which is 

 split off by alkali from chlorophyll, is called " chlorophyllin," and contains 

 magnesium. Its derivatives are the "phyllins." These latter are produced 

 by further action of alkali, which splits off carboxyl groups. These phyllins still 

 contain the magnesium, which is combined with the nitrogens of four pyrrol 

 groups. To split off the magnesium from them acid is necessary, and we then 

 obtain the " porphyrins." Thus : 



Chlorophyll a 

 (by acid) (by alkali) 



Magnesium + pb.<eophy tin a phytol + chlorophyllin (contains Mg) 



(by alkali) (by alkali at 200) 



phytochlorin + phytol phyllins 



(by acid) 



porphyrins + Mg 



The porphyrins are of interest, because they serve to bring into connection 

 chlorophyll and hcemoglobin. The blood pigment seems to be a derivative of a 

 substance which contains iron united to four pyrrol groups in a way similar to the 

 magnesium of chlorophyll (see Kiister's paper, 1908, and the book of Willstiitter 

 and Stoll, 1913, pp. 42 and 39). Hoppe-Seyler (1880, p. 201) described a 

 compound, which he called " phylloporphyrin," obtained from chlorophyll, which 

 gave the same absorption spectrum as the haematoporphyrin derived from 

 haemoglobin. Similar pyrrol derivatives have been obtained from both. 



If one of the porphyrins, obtained by the action of acid on phyllins, be heated 

 with soda-lime, " jetioporphyrin " is formed ; it turns out to be the same substance 

 as that which is formed from haematoporphyrin by similar treatment. Now 

 haematoporphyrin is formed from haematin, which is haemoglobin minus its protein 

 component, by the removal of iron by acid, as magnesium is removed from phyllin 

 by acid. To form haemoglobin, haematin combines with a protein, globin ; to 

 form chlorophyll, phyllin, or a carboxylic acid derived from it, combines with 

 an alcohol, phytol, to form an ester. Chlorophyll, however, loses its magnesium 

 more readily than haemoglobin does its iron. 



As regards the pyrrol constituents of the two pigments, information is to 

 be obtained by oxidation. Kiister (1900) obtained, by oxidation of haemin 

 ( = haematin hydrochloride), an imide of an acid, which he called htematinic acid. 

 Willstiitter finds that chlorophyll behaves in a similar way. The porphyrins 



