Regulation of Purine Nucleotide Synthesis in Bacillus subtilis II. Specificity of Purine Derivatives for Enzyme Repression*

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Abstract
1. For the study of the specificity of purine derivatives to the repression of five enzymes involved in the purine nucleotide biosynthetic pathway, several mutant strains, which did not convert the test purine derivatives to the other type of purines, were derived from purine requiring mutants of B. subtilis Marburg. 2. IMP dehydrogenase [EC 1.2.1.14], an enzyme involved in the formation of GMP, was repressed only by guanosine and not repressed by adenosine, xanthosine and inosine. 3. AdenyLosuccinate synthetase [EC 6.3.4. 4], an enzyme forming AMP, was repressed only by adenosine but neither by guanosine, mo- sine, nor xanthosine. 4. IMP transforinylase and phosphoribosyl pyrophosphate amidotransferase [EC 2.4.2. 14], the enzymes forming IMP, a common precursor of both AMP and GMP, were repressed by adenosine or guanosine, slightly by inosine but not by xanthosine. 5. Adenylosuccinate lyase [EC 4.3.2.2], an enzyme forming IMP as well as forming AMP, was repressed by adenosine or guanosine, slightly by inosine but not by xanthosine. Based on these results, the repression in puriie nucleotide biosynthesis was discussed to be rational as the regulator control mechanism.