PORPHYRINS 



265 



The structure of the porphyrin associated with A cytochromes is as yet unknown. It ap- 

 parently has a formyl side chain and a large alkyl side chain. 



Other porphyrins related structurally to this group are occasionally found and prob- 

 ably represent precursors. Hence their structures are given in the section on biosynthe- 

 sis. 



TABLE 1. NOMENCLATURE OF SOME IRON 

 PROTOPORPHYRIN DERIVATIVES 



CHLOROPHYLL AND RELATED COMPOUNDS 



Chlorophylls a and b are the only green pigments of all plants higher than the algae. 

 The ratio of chlorophyll a to b is usually about 3: 1, and there is no ready interconversion 

 between them. The structure is given for chlorophyll a. Chlorophyll b has a formyl 

 group instead of methyl at position 3: 



Wis, 



o=c 



I 



Y"2 OCH3 



OC20H 



39 



