Figure 1.

Thiamin biosynthesis in higher plants. (a) Chemical structure of thiamin. (b) Thiamin biosynthesis requires steps in the chloroplast, cytosol, and the mitochondria. AIR, 5-aminoimidazole ribonucleotide; Gly, glycine; HET-P, 4-methyl-5-β-hydroxyethylthiazole phosphate; HMP-P, 4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate; HMP-PP, 4-amino-2-methyl-5-hydroxymethylpyrimidine diphosphate; TH1, HMP-P kinase/TMP pyrophosphorylase; THI1, HET-P synthase; TH2, TMP phosphatase; THIC, HMP-P synthase; TMP, thiamin monophosphate; TPK, thiamin pyrophosphokinase.