250 



Essays in Biochemistry 



Tricarboxylic 

 Acid 

 Cycle 



\ x^. Succinyl X / 



\f? Co/ Y 

 ^M \ cv-K. 



Ureido group of purines, 

 formate, etc. 



the a- carbon atom to 



[HOOC - CH, - CH 2 - C - CHO] 

 II 

 

 Ketoglutaraldehyde 



/fOJ 



HOOC - CH, - CH, - C - COOH 



" II 



o 



- Ketoglutarate 

 Succinate\ I 



^ s ^ + Glycine 



\ H 



Succinate - HOOC - CH , - CH 2 - C - C - COOH 

 Glycine 1 1 | 



Cycle NH 2 



a-Amino-/3-ketoadipic acid (I) 



/ 



CO, 



HOOC - CH 2 - CH, - C - CH,NH. 



* II 

 O 

 6 -Aminolevulinic acid (II) 



Porphyrin 



a-Ketoglutaric acid 

 Fin. 7. Succinate-glycine cycle: a pathway for the metabolism of glycine. 



COOH 

 I 

 COOH CH 2 



I I 

 CH, CH, 



I I 

 CH 2 + C = O 



C = C*H, 



CH, / 

 | " H 2 N 

 NH 2 



5- Aminolevulinic 



acid 



(II) + (ID 



-2H,0 



COOH 

 I 

 COOH CH 2 

 I I 



CH, CH 9 



Protoporphyrin 



C*H 2 g 

 NH, 



Precursor 

 pyrrole 



Fig. 8. The mechanism for the formation of the monopyrrole, porphobilinogen, 

 by condensation of two moles of 5-aminolevulinic acid. The carbon atoms bear- 

 ing the closed circles (•) were originally the a-carbon atom of glycine. 



