BIOSYNTHESIS OF AMINO ACIDS 



77 



COOH 



I 

 CHg 



I 

 CH, 



I 

 CO 



I 



COOH 



*COOH 



COOH 

 I 

 CH, 



I 

 CH, 



-HzO 



HOOC-C-OH 



I 



CHj-COOH 



COOH 



I 

 CH, 



I 

 CH, 



I 

 C-COOH 



II 

 CH 



J 

 XOOH 



*COOH 



I 

 (CHj)^ 



HP HC-COOH 



-^ I 



CHOH 



*COOH 



Homoisocitrate 



, 2H 



COOH 



i „ „ I 

 (CH2)3 - NH2 (CH,),^ 



COOH 



<2)3 



-C02 



-2H 



CHNH2 



*COOH 



a- Aminoodipate 



CO 



*COOH 



a- Ketoadipate 



a-Ketoglutaric 



*CHO 



I 

 (CHJ, 



I 

 CH-NH2 



*COOH 



"NHj 



'CH,-NH, 

 I 



(CH2)3 



CH-NHz 



COOH 



Lysine 



Fig. 34. Postulated pathway of lysine biosynthesis. 



that a-ketoadipic acid and a-aminoadipic acid may be formed from homocitrate by a 

 series of reactions analogous to those which take place In the citric acid cycle (Fig. 34). 

 Not Inconsistent with this scheme is the observation that acetate- i-'-'C is a precursor 

 primarily of carbons one and six of Torulopsis lysine whereas acetate-Q-'^iC Is Incorporated 

 into carbons 2-5 of lysine. The radioactivity of carbon 2 Is however nearly twice as great 

 as that of carbons 3-5 and that of carbon 6 Is about two thirds of carbon i. The radioactivity 

 of carbons 3-6 resemble closely that to be expected from the succinyl moiety of a-keto- 

 glutarate. Neurospora extracts contain an enzyme which catalyzes a transamination reaction 

 between a-aminoadipic acid and a-ketoglutarate (Ames and Horecker, 1956). 



Diaminopimelic pathway of E. coli. c/l., s-Diaminopimelic acid occurs in the 

 protein of £■. coli (Dewey et al., 1954). A pyridoxal phosphate requiring enzyme 

 exists in this organism and in Aerobacter which catalyzes the decarboxylation of 



CH2— CH — COOH CHg— CHj— NHa 



CH2 NH2 -CO2 , CHa 



CHj— CH — COOH CHa— CH COOH 



NH2 NHg 



Diaminopimelic Lysine 



Fig. 35. Decarboxylation of diaminopimelic acid to lysine. 



Literature p. 124 



