PORPHYRINS 



appears that all the porphyrins in nature, including chlorophyll, 

 in all different types of cells are synthesized by the same basic 

 pathway. The different porphyrins merely arise by modifica- 

 tions occurring in the side chains in the /3-positions of the pyrrole 

 units. 



^, \ cC-KETO GLUTARATE 



UREIDO group of purines, ^SUCCiNATSE 



formate, etc 



the al-corbon atom t 



rr 



MNE I 



Glycine 



SUCCINATE- H 



GLYCINE HOOC-CH2-CH2-C-C-COOH 

 CYCLE 



hOOC-CH2-CH2-C-CHo] 







keto-glufaroldehyde 



II I 



IMH2 

 cX-amino-p- kefo adipic acid(I) 



} 



CO 



■2 



\[0] 



HOOC-CH2-CH2-C-CH2NH2 

 - amino - levulinic ocid(ir) 



HOOC-CHo-CHp-C-COOH 

 '• '-II 







C<-ke?o-qlutoric acid 



I 



PORPHYRIN 



Fig. 1. Succinate -glycine cycle: a pathway for the metabolism of glycine 



(28,29). 



The problem of the biosynthesis of porphyrins, in the for- 

 mation of the initial intermediates, can be considered, from a 

 more general point of view, to be merely one aspect of the metab- 

 olism of glycine. Many over-all aspects of glycine metabolism 

 are now known, and especially the metabolic pattern of the 

 a-carbon atom of glycine in its utilization for the synthesis of 

 other compounds has been established. The a-carbon atom of 



519 



