Studies on peroxisomes. V. Effects of ethyl p-chlorophenoxyisobutyrate on the centrifugal behavior of rat liver peroxisomes.:V. Effect of Ethyl <i>p</i>-Chlorophenoxyisobutyrate on the Centrifugal Behavior of Rat Liver Peroxisomes

After Wistar male rats had been fed on a diet containing 0.25% of ethyl p-chloro-phenoxyisobutyrate (CPIB) for 28 days, changes in the enzyme activities and centrif-ugal behavior of rat liver peroxisomes were investigated. (1) Compared with control rats fed on the basal diet, the catalase [EC 1. 11. 1. 6] activity of rat livers after the administration of CPIB increased about 2.5-fold, while urate oxidase [EC 1. 7. 3. 3] activity did not change significantly. Though D-amino acid oxidase [EC 1. 4. 3. 3] activity markedly decresed to approximately one-sixth of the control, the activity of L-α-hydroxy acid oxidase [EC 1. 1. 3. 15], a flavin enzyme like D-amino acid oxidase, was not affected significantly after the administration of CPIB. (2) When the hepatic cells of CPIB-treated rats were fractionated by differential centrifugation, most of the increase of catalase activity appeared in the supernatant fraction. A decrease in the hepatic D-amino acid oxidase activity of CPIB-treated rats was observed in all the fractions. As for the subcellular distribution of the particle-bound enzymes, the specific activities of both catalase and urate oxidase of CPIB-treated rat livers were higher in the light mitochondrial fraction than in other fractions. (3) Sedimentation patterns in a sucrose density gradient did not show any difference between normal peroxisomes and CPIB-treated ones. (4) In the case of CPIB-treated rats, studies of their sedimentation patterns by Ficoll density gradient centrifugation showed two main particulate peaks containing both catalase and urate oxidase, although only a single peak was observed in the case of control rats.