122 



UNITY AND DIVERSITY IN BIOCHEMISTRY 



When the phytol is separated from a chlorophyll in acetone solution, the 

 green compound remaining is a chlorophylline. 



The formula below shows that the chlorophylls are magnesium com- 

 plexes of a modified porphin structure, isomeric with protoporphyrin. 

 Chlorophyll-^ and chlorophyll-6 are present in green plants and the green 

 algae. Chlorophyll-6 differs from chlorophyll-a by replacement of a methyl 

 group in position 3 by a formyl group. The structures of chlorophylls c 

 and d are still not completely known. The brown algae contain chlorophylls 

 a and c, and the red algae chlorophylls a and d. 



Bacteriochlorophyll, which is present in the purple bacteria, differs from 

 chlorophyll-a in two respects : 



H CH, \ H 



I c-c=o 



HsoQoOOC— CH, I 



COOCH, 



Phytol 



Chlorophyll-a 



the replacement of a vinyl group by acetyl, and the reduction of ring II to 

 a dihydropyrrol structure. 



If the magnesium is removed from chlorophyll, a phaeophytin is left, and 

 if, in addition, the phytol is removed then the remaining fragment is 

 named a "phaeophorbide", and has the same structure as porphyrin, apart 

 from the presence of two extra hydrogen atoms and a resulting redistribu- 

 tion of double bonds. 



In the grana of leaves, the chlorophylls are associated with proteins to 

 form complex macromolecules whose nature is still obscure. 



{c) Metalloflavoproteins 



Flavin phosphate (FP) or flavin mononucleotide (FMN) (see p. 69) 

 exist in combination with protein, in a macromolecular form which bears 

 the name "old yellow enzyme", thus called because others have since been 



