Abstract
It has been proposed by several groups of investigators that the pyrimidine moiety of thiamin is synthesized via 5-aminoimidazole ribotide, an intermediate of purine biosynthetic route in bacteria. To decide whether the methyl group attached to C-2 atom of the pyrimidine is introduced after the recyclization of the imidazole ring of 5-amino-imidazole ribotide (AIR) to the pyrimidine, the competition of radioactive formate incorporation into the pyrimidine moiety by 4-amino-5-hydroxy-methylpyrimidine was investigated. The results showed that this compound was not used as a biosynthetic intermediate by Escherichia coli and Saccharomyces cerevisiae. It remains unsolved, at which step methyl group is introduced and which compound is methyl origin of the pyrimidine moiety of thiamin.
