Figure 13.

The C3 Cycle Showing Relationships to the Isoprenoid and Thiamine Pathways.

Thiamine biosynthesis (red typeface) is formed from two moieties, HMPP and HETP, that are biosynthesized from compounds arising from the C3 cycle, ribose 5-phosphate (R5P), and G3P. These two compounds are a product and substrate, respectively, of the reactions performed by TK. Thiamine monophosphate is generated from the condensation of HETP and HMPP. Thiamine monophosphate is dephosphorylated to thiamine, which is transported to the cytosol where it undergoes phosphorylation to TPP. TPP can bind to the riboswitch regulatory mechanism of ThiC located in the 3′ UTR of nascent mRNA in the nucleus, resulting in a reduction of biosynthesis of the ThiC protein and in turn the biosynthesis of thiamine. TPP-requiring enzymes are shown in bold in dark blue.