Figure 2

Intracellular thiamine homeostasis is initially achieved through the uptake of thiamine (T) by the thiamine transporters THTR1 and THTR2. Once inside the cell, thiamine is converted to the active co-enzyme, thiamine pyrophosphate (TPP) by thiamine pyrophosphokinase-1 (TPK1). Thiamine can than function as a cofactor for the cytoplasmic TKT. Transport of TPP by the thiamine pyrophosphate carrier (TPC) across the mitochondrial membrane supplies cofactor for activity of pyruvate dehydrogenase (PDH) and alpha-ketoglutarate dehydrogenase (α-KGDH). Intracellular TPP can also be converted to thiamine monophosphate (TMP) by thiamine pyrophosphatase (TPPase) and subsequently recycled back to thiamine by thiamine monophosphatase (TMPase). Both TMP and TPP can be effluxed out of the cell through the reduced folate carrier (RFC1).