Pfizer Handbook of Microbial Metabolites 308 



priate auxotrophs and can be isolated. This scheme has been 

 found in a variety of molds, yeasts and bacteria. 



Ornithine reacts with carbamyl phosphate to form citrulline, 

 an intermediate in the biosynthesis of arginine: 



H2N— CH2— CH2— CH2— CH— COOH 



I 



NH2 

 Ornithine 



O 



I H2N— C— O— PO3H2 



o 



II 



H2N— C— NH— CH2— CH2— CH2— CH— COOH 



I 

 NH2 



Citrulline 



HOOC— CH— CH2— COOH 



NH2 



e 



00c— CH—CH2— COOH 



I 

 ©NH 



H2N— C— NH— CH2— CH2— CH2— CH— COOH 



I 

 NH2 



Argininosuccinate 



^ > HOOC— CH=CH— COOH 



NH ^ 



II 

 H2N— C— NH— CH2— CH2— CH2— CH— COOH 



I 



NH2 

 Arginine 



Arginine can complete the "urea cycle" by losing urea to form 

 ornithine. Enzymes for all these steps have been found in var- 

 ious microorganisms. 



Glutamic acid acts as an ammonia carrier by formation of its 

 half amide, glutamine, and in this way contributes nitrogen to 

 the biosynthesis of purines and amino sugars. 



Aspartic acid also occupies a central position in nitrogen 

 metabolism. In microorganisms it can be synthesized either by 

 amination of oxaloacetic acid or by the addition of ammonia 



