Thiamine metabolic pathways (Homo sapiens)

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Thiamine enters the cell through THTRI and THTR2 receptors encoded by SLCI9A2 and SLC19A3 genes, respectively. It is then converted into thiamine pyrophosphate (TPP) by the thiamine phosphokinase enzyme encoded by TPK1 (5). TPP enters the mitochondria through the TPP transporter (TPP tr) encoded by the SLC25A19 gene. In the mitochondria, TPP serves as a cofactor for ketoglutarate-(2),pyruvate-(1) and branched-chain a-keto acid (3) dehydrogenases that are involved in the mitochondrial energy production from carbohydrates and amino acids. In the cytosol, TPP is a cofactor of the transketolase (4) in the pentose phosphate pathway. This pathway leads to the production of NAPDH, an important cofactor in biosynthetic pathways, as well as important intermediary molecules such as ribose 5-phosphate needed for the synthesis of nucleic acids and GA3P for the synthesis of complex lipids including plasmalogens, sphingolipids, and phospholipids. (Adapted from Lamari et al. (2013)). (Blau, CH15)