470 



THE BIOCHEMISTRY OF B VITAMINS 



offered by inhibition analysis, which allows some insight into the meta- 

 bolic functions of this and related vitamins. 



Sulfanilamide, in preventing the functioning of p-aminobenzoic acid 

 in Escherichia coli, inhibits a series of biochemical transformations, as 

 indicated in Figure 6. 5, 37, 3S The inhibition index determined in a salts- 



HS— CH 2 



NH 2 

 -CH 2 — CH— COOH 



Inhibition NH 2 

 Index 

 > CH 3 — S— CH 2 — CH 2 — CH— COOH 



Homocysteine (or related 

 precursor) 



3000 



Methionine 



// 

 NH 2 — C 



I 

 C— N 



II /' 

 NH 2 — C— NH 



CH 



5(4)-Amino-4(5)-imidazolecarbox- 

 amide (or derivative) 



O 



NH 2 — CH 2 — C— OH 



Glycine 



10,000 



30,000 



HN 



I 

 HC 



C 



I 



c- 



N— C- 



>CH 

 -NH 



Hypoxanthine 



Xanthine 



Adenine 



Guanine 



or derivatives 



NH 2 



HOCH 2 — CH— COOH 



Serine 



CH 3 



OH NH 2 

 -CH— CH— COOH 



Threonine 



Precursor 



100,000 



NH— C 

 NH— CH 



-CH 3 



Thymine 

 (or derivative, 

 e.g., thymidine) 



Figure 6, Interrelationships Involving p-Aminobenzoic Acid Determined by 

 Inhibition Analysis with Sulfanilamide 



glucose medium is approximately 3000; but in the presence of supple- 

 ments of methionine a higher ratio, approximately 10,000, is required for 

 the same degree of inhibition of growth of the organism. 37 The inhibition 

 is further affected by certain purines, which are ineffective in the absence 

 of supplementary methionine. 37 The inhibition index is approximately 

 30,000 when determined in a medium containing both methionine and 

 purines. The purines and derivatives effective in replacing the purine 



