98 growth: synthesis of bacterial protoplasm 



out witli Esch. coli and tlie last four steps confirmed in 

 Neurospora: 



SO4 



t ?"= 



" ?^ Pyruvic acid 



SO3 ! ' 



I COOH 



->► SH CH2OH 



I I 



CHj CHj L, 



I -L I Momosenne 



Cysteine chnh, chnh, 

 II 



COOH COOH 



CH,-S CH, CHjSH CHj-S-CHj 



II I I 



Cu Ki i_i CH7 CH? CH? 



HNH2 I ^ j,^ I ^ 3^ I 



I CHNH^ CHNH2 CHNH2 



COOH I I I 



COOH COOH COOH 



Cystathionine Honnocysteine Methionine 



Biocliemical mutant studies with Neurospora have shown 

 that the biosynthetic precursors of tryptophan are anthranilic 

 acid and indole, and that the last step involves the condensation 

 of indole with serine. This condensation has been further 

 proved by the preparation of a cell-free enzyme which accom- 

 plished the synthesis in the presence of pyridoxal phosphate as 

 prosthetic group : 



COOH >^ CH,OH 



I ^^" r n iCH^-CHNHj-COOH 



CHNH, ^ ' " ' 



N 



COOH 



KAJ 



Anthranilic Indole Serine. Tryptophan. 



acid. 



