Observations on the biosynthesis of thiamine in yeast

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Abstract
Methods are described for the isolation of radioactively pure thiamine from yeast and its degradation on a small scale to its cyclic components. A degradation of the pyrimidine ring and a thin-layer method for the separation of thiamine, its derivatives and pyrimidine and thiazole residues are described. [C14]Formate is more effectively incorporated into the pyrimidine residue than into the thiazole residue, whereas the reverse is true with L-[Me-C14]methionine. Experiments with [Me-C14, S35]methionine demostrate that methionine provides an intact unit for the biosynthesis of the thiazole ring. [6-C14]Orotic acid is insignificantly incorporated into the pyrimidine residue of thiamine. Experiments with [1-C14]- and [2-C14]-acetate indicate that it is incorporated as a unit into the thiazole residue, but that only C-2 is incorporated into the pyrimidine residue. L-[U-C14] Alanine is also effectively incorporated into the thiazole residue. These results are discussed in relation to possible pathways of biosynthesis of the two ring components of the thiamine molecule.