278 



H. H. PLOUGH 



Table 17.3, some cysteine requiring strains will overgrow the parent and this 

 may be due to differences in energy requirements. 



The second set of steps in synthesis being studied concerns the adenine 

 requirer. Here we appear to have rather more definite information than was 

 described by Guthrie (1949) for the purine auxotrophs of E. coli. It has been 

 shown that the Salmonella auxotroph utilizes adenine and hypoxanthine, but 

 not guanine and xanthine. Of the nucleosides and nucleotides only adenosine 

 and adenylic acid are used, and much more of the latter is required for com- 

 parable growth than of adenine. Thus it appears that in purine metabolism, 

 Salmonella and an animal like Tetrahymena (Kidder and Dewey, 1948) 

 show almost opposite requirements, for the bacteria do not convert adenine 

 to guanine. Preliminary studies by Mrs. Helen Y. Miller demonstrate a spar- 

 ing action for adenine utilization by the amino acid histidine. This suggests 



N==C-NH2 



HC— NH 



HC— NH 



H-C 



C-NH 



N 



— C-N 



Adenine 



^ 



CH 



C— N 

 CH2 



o=c 



^ 



CH 



-^- 



C — N 

 CH2 

 H2N-CH 



/- 



:cH 



COOH 



Imidazole Pyruvic Acid 



+ 

 Pyridoxamine 



COOH 

 Histidine 



Fig. 17.5 — A Possible relation of Adenine to Histidine synthesis (after Broquist and Snell). 



that for this organism as with Lactobacillus (Broquist and Snell, 1949) the 

 purine is a precursor of histidine, probably by the utilization of the imid- 

 azole ring through pyruvic acid, and the transaminating action of pyridoxa- 

 mine (Figure 17.5). While these facts have been revealed by a study of the 

 adenine mutant alone, further gene changes and their reactions with the 

 histidine auxotrophs already available should help clarify some of the inter- 

 actions of purines and amino acids in the bacterial cell. 



ALTERATION OF ANTIGENIC SPECIFICITY 



The auxotrophic mutations reveal a series of biochemical steps or trans- 

 formations common to whole groups of organisms. Antigenic analysis, on the 

 other hand, has revealed precise specific or strain differences which are as 

 distinctive as the form or structural differences of complex animals and 

 plants. This has been clearly demonstrated by the blood group analysis 

 presented in the studies of Irwin and his colleagues. The specificity is no less 



