Abstract
The biosynthetic pathway of the thiazole and the pyrimidine portion of thiamin in eukaryote was studied. The nitrogen atom of glycine was incorporated into the thiazole in the aerobic microorganisms. The nitrogen atom of tyrosine was incorporated into the thiazole in the facultative anaerobic organiSmS. The biosynthetic route of thiazole is different between aerobic and facultative anaerobic organiSmS. The sulfur atom of thiazole was derived from cysteine and the C-4', 4, 5, 5', 5" atoms of the thiazole is derived from C-2, 3, 4, 5, 6 atoms of glucose, respectively in eukaryoteS. The incorporation of ^<15>NH_4C1 into the pyrimidine in S. cerevisiae was inhibited by histidine. The label of DL-[ring-^15N_2]histidine was incorporated directly into the pyrimidine. The N-_τand N-_πatoms of histidine were incorporated into the N-3 and amino-N of the pyrimidine, respectively. The ring C-2 of histidine was incorporated into the C-4 of the pyrimidine and the incorporation of [^<13>C] formate was diluted by histidine. The N-_τ, C-2 and N-_π atoms of histidine were incorporated into the N-3, C-4 and amino-N at C-4 of the pyrimidine as a single unit. The incorporation of ^<15>NH_4C1 into the N-1 of the pyrimidine was inhibited by pyridoxine, a trace constituent of the medium in S. cerevisiae. The labeled [2'-^<13>C]-, [^<15>N]-, [6-^<13>C]- and [5'-^2H_2] pyridoxine were chemically synthesized and were incorporated into the C-2', N-1, C-6 and H_2-5' of the pyrimidine, respectively. These findings suggested that the pyrimidine was synthesized from histidine and pyridoxine in eukaryotes. The origin of the N atom of pyridoxine was studied. The N-atom of pyridoxine was derived from amide-N atom of glutamine in S. cerevisiae. The amide-N atom of glutamine was not incorporated into pyridoxine in E. coli. The biosynthetic route of pyridoxine might be different between eukaryotes and prokaryotes.
