535 



Purines 



CH3 CH 



HOCH 



NH2 



HOCH2 



Substitution of other amino acids for the p-methoxy- 

 phenylalanine moiety gives analogues which still inhibit 

 protein synthesis, although the free nucleoside moiety 

 is a less effective inhibitor. The similarity in structure 

 suggests competition with adenine nucleoside. 



Functions of coenzyme A have been discussed through- 

 out the appropriate sections. The biosyntheses of the 

 various moieties of the molecule also have been consid- 

 ered with the possible exception of ^-aminoethanethiol, 

 which is derived from cysteine. 



The biosynthetic union of these moieties, originally 

 studied in animal tissues, follows the probable course: 



CH3 OH 



HOCH2— C CH— COOH 



CH3 

 Pantoic Acid 



+ HoN— CHo— CH2— COOH 



^ATP 

 — >ADP 



^-Alanine 



