Thiamine is used in a variety of metabolic pathways in the form of thiamine pyrophosphate, or Vitamin B1. Its use is primarily as a cofactor for enzymes in key metabolic reactions. In plants, 5-aminoimidazole ribonucleotide, a product from purine metabolism, reacts with S-adenosylmethionine to produce 4-amino-5-hydroxymethyl-2-methylpyrimidine phosphate in the chloroplast. With the help of a TH1 enzyme, this compound reacts to form 4-amino-5-hydroxymethyl-2-methylpyrimidine diphosphate, dephosphorylating ATP in the process. This diphosphate compound is then further broken down into thiamine monophosphate by reacting with a number of complex compounds, two of which are derived from reactions using Glycine and 5-(2-hydroxymethyl)-4-methylthiazole, respectively. The thiamine monophosphate is then transported out of the chloroplast into the cytoplasm, where it is hydrolysed to form thiamine. Thiamine is now phosphorylated through a pair of reactions to form thiamine triphosphate. Alternatively, thiamine undergoes unknown reaction(s) to form N-formyl-4-amino-5-aminomethyl-2-methylpyrimidine, which, after being hydrolysed twice, is transported back into the chloroplast and reacts to form the earlier compound 4-amino-5-hydroxymethyl-2-methylpyrimidine phosphate. Notedly, many of the compounds used in thiamine metabolism are modified products of other crucial metabolic pathways, including glycine metabolism, cysteine metabolism, and glycolysis.

Thiamine Metabolism References