RAT-LIVER MITOCHONDRIA CAN HYDROLYZE THIAMINE PYROPHOSPHATE TO THIAMINE MONOPHOSPHATE WHICH CAN CROSS THE MITOCHONDRIAL-MEMBRANE IN A CARRIER-MEDIATED PROCESS

We show here that TPP --> TMP conversion can take place in rat liver m itochondria. This occurs via the novel, putative TPP pyrophosphatase l ocalised in the mitochondrial matrix, as shown both by digitonin titra tion and by an HPLC enzyme assay carried out on the mitochondrial matr ix fraction. Certain features of the reaction, including the substrate and pH dependence, are reported, Additional evidence is given that ex ternally added TMP can cross the mitochondrial membrane in a manner co nsistent,vith the occurrence of a carrier-mediated process. This can o ccur both via the TPP translocator and via a novel translocator, inhib ited by CAT but different from the ADP/ATP carrier. (C) 1998 Federatio n of European Biochemical Societies.