抄録
The pyrimidine moiety of thiamin is biosynthesized in Escherichia coli by the different route under anaerobic conditions from that under aerobic conditions. [^<15>N] Pantothenate which was reported to be the precursor of the pyrimidine under anaerobic conditions by Downs, was chemically synthesized as a tracer. [^<15>N] Pantothenate was not incorporated into the pyrimidine in E. coli under anaerobic conditions. To elucidate the precursors of the pyrimidine under anaerobic conditions, the competitive experiments between [^<15>N] ammonium salts and ^<14>N-amino acids were carried out. The ^<15>N incorporation into the pyrimidine was inhibited by glycine, the precursor of the pyrimidine under aerobic conditions. The N atom of glycine were incorporated into the same locations in the pyrimidine under aerobic conditions. Furthermore, amide-N atom of L-glutamine, which was incorporated into the N-3 and amino-N of the pyrimidine under aerobic conditions, was not incorporated into the N-3 of the pyrimidine but only into the amino-N atom at C-4 of the pyrimidine. We reported already that formate, the precursor of C-2 of the pyrimidine under aerobic conditions was not incorporated under anaerobic conditions. These results suggested that the pyrimidine was synthesized from 5-aminoimidazole ribonucleotide (AIR) same as the route under aerobic conditions. However, the two precursors from 5-phosphoribosyl-1-pyrophosphate to AIR in the purine nucleotide biosynthesis could be changed under anaerobic conditions.
