Subcellular Localization of Dihydropyrimidine Dehydrogenase

Although dihydropyrimidine dehydrogenase (DPD) has been purified and characterized from liver tissues of various mammals conflicting data exist on its subcellular localization. To determine the localization of DPD we prepared crude subcellular fractions of a rat liver homogenate by means of differential centrifugation. In the fractions obtained (heavy mitochondrial, light mitochondrial, microsomal and cytosolic) the activities of different marker enzymes were measured as well as the activity of DPD. These results showed that almost all of the activity of DPD was located in the cytosolic fraction. To exclude any particulate-associated DPD, a light mitochondrial fraction was subsequently subjected to equilibrium density gradient centrifugation. The distribution profile of the activity of DPD and the various marker enzymes indicated that DPD from rat liver was exclusively located in the cytosol since no significant activity of DPD could be detected in any subcellular organelle.