Abstract
Biosynthetic pathways of the pyrimidine moiety and thiazole moiety of thiamin were studied. Procaryotes and eucaryotes have different biosynthetic pathways for the pyrimidine. In procaryotes, the pyrimidine is formed by ring expansion of imidazole accompanied insertion of C-4', C-5' fragment of ribose of 5-aminoimidazole ribonucleotide, an intermediate of purine biosynthesis. In eucaryotes, N-3, C-4, and amino-N attached at C-4 of the pyrimidine are derived from N-1, C-2 and N-3 of the imidazole ring of histidine and the three carbon unit of C-6, C-5 and C-7 is originated from C-1, C-2 and C-3 of ribose. The precursor of C-2 and N-3 of the thiazole moiety is tyrosine in anaerobic microorganisms and glycine in aerobic microorganisms. Anaerobic microorganisms and aerobic microorganisms have different biosynthetic pathways for the thiazole. The origin of the S atom was established as being the S atom of cysteine in Escherichia coli and Saccharomyces cerevisiae. The origin of 5-carbons chain, C-4', 4, 5, 5' and 5" of the thiazole in anaerobic microorganisms was the compound drived from pyruvate and glycerol. The 5-carbons chain is derived from glucose via pentose phosphate shunt in aerobic microorganisms.
