HOOC~CHo~'CHo"*C~CHp 

 NH2 

 S AMINO LEVULINIC ACID 



CO2H 

 GLYCINE 



COjH 

 CH2 



I 



CO2H 

 CHp 



CH2. 

 C=0 

 I 

 ,CH2 



HgC 



NH, 



NH2 



CC^HCHg 



Ch^CHgCOgH 



^. 



COgHCHg^^^y^CHgCOgH 



f^ 



CH2 



ccyn 



CH2 



CH, 



"^ 



CH2f^2(j;H2 



CH? 

 I 



NH2 

 PORPHOBILINOCeN (PBG) 



CH2 

 UROPORPHYRINOGEN M 



I DECARBOXYLATIONS 

 I DEHYDROGENATIONS 



PROTOPORPHYRIN - 9 

 F. + + 



HEME 



Mg' 



RING 3Z: 

 .* FORMATION 



• Mg PROTOPORPHYRIN -► — — 



Vi = -CH=CH2 



Pr = -CH2-CH2-CO2H 



Mt' -CH3 



PHYTOL' 



CHLOROPHYLL 



Figure 11. The biosynthesis of porphyrins. 



is formed from the cycle by carboxylation of phosphoenolpy- 

 ruvate, derived from phosphoglycerate. 



Another, and perhaps more likely route to succinate is 

 via reductive carboxylation to form malate, dehydration, and 

 reduction of malate to give succinate. 



63 



