IV. HIOCHEMICAL SYSTEMS 131 



It is iiilcrcsliiii;, howcvci', lliat no l-aiiiiiio-o-imidazolccjirhoxiiinidc lias 

 Ix'cii (lotocted ill crltures of L. casei grown with inliihitory coiKX'nl rat ions 

 of "x methyl P(JA" in the presence of some purine.^ This is not at all 

 surprising when one ccnisiders that both the C^ and the C^ atoms of the 

 purine ring are introduced as 1-carlion fragments. If the introduction of the 

 C^-carbon happens to be the first limiting reaction, then the imidazole- 

 carboxamide would not be expected to accumulate. It is ineffective as a 

 growth promoter for nine purine-less mutants of E. coli but is effective for 

 one mutant at tiic high level of 100 to 200 7 per milliliter, which is about 

 fifteen times as high as the level of purine required to give the same ef- 

 fect.^^'-" Another mutant was found which accumulates the amine when 

 grown in the presence of a purine. With 5 7 of xanthine per milliliter, growth 

 is approximately half of maximum, and 11.3 7 of aminoimidazolecarboxam- 

 ide accumulates per milliliter of medium. •^ 



A sj^iergistic effect was observed between purine and aminoimidazole- 

 carboxamide.-" In the presence of only 4 7 of any purine per milliliter, 

 which by itself gives only 30 % growth, 30 7 of aminoimidazolecarboxamide 

 per millihter gives maximum growth. Formylaminoimidazolecarboxamide 

 which contains the "missing" carbon atom, but not in the form of the 

 closed pyrimidine ring, is more active than the parent amine. Vitamin B12 

 (0.2 m7 per milliliter) increased growth of the purine-less E. coli mutant 

 and increased utilization of added aminoimidazolecarboxamide. p-x\mino- 

 benzoic acid (0.1 7 per milhliter) increased growth but did not increase utili- 

 zation of the imidazole derivative.^" 



The activity of vitamin Bio in increasing the utilization of amine is of 

 special interest. Shive has found^^ that vitamin B12 increases the inhibition 

 ratio of sulfanilamide with E. coli at the inhibition levels for methionine, 

 purine, and serine synthesis. The non-specific effect of vitamin B12 in this 

 case was explained on the basis that B12 aids in the conversion of p-amino- 

 benzoic acid to the active coenzyme. 



An alternate explanation for the activity of vitamin B12 is that it facili- 

 tates the conversion of the imidazole derivative to a desoxyriboside. Certain 

 lactic acid bacteria requiring vitamin B12 are able to utilize thymine desoxy- 

 riboside or purine desoxy ribosides but not free thymine. Under these cir- 

 cumstances the function of vitamin B12 appears to be synthesis of a desoxy- 

 ribose derivative capable of attachment to thj^mine. The recent work of 

 Greenberg--' -^ has shown that ring closure in a pigeon liver system does not 



lU. S. Gots, Arch. Biochem. 29, 222 (1950). 



2" Ruth Ben-Ishai, B. Volcani, and E. D. Bergmann, Arch. Biochem. and Biophys. 32, 



229 (1951). 

 *' W. Shive, Vitamins and Hormones 9, 75 (1951). 

 " G. R. Greenberg, Federation Proc. 9, 179 (1950). 

 " G. R. Greenberg, ./. Biol. Chem. 190, Gil (1951). 



