Scheme 1. Proposed scheme for thiamine and TDP biosynthesis in Eukaryota.

The biosynthesis pathways may differ in some details between yeasts and higher plants, as exemplified by different substrates (*) used by plants for the synthesis of the thiazole moiety HET-P. The sequenced genes in bold and purified proteins (italics) unequivocally assigned to thiamine biosynthesis (normal font) are shown. The symbols of proteins whose three-dimensional structures were reported are in higher plants (underlined) and bakers yeast. A, A. thaliana; Z, Z. mays; b, B. napus; ag, A. glutinosa.