After Wistar male rats had been fed on a diet containing 0.25of ethylp-choro-phenoxyisobutyrate (CPIB) for 28 days, changes in the enzyme activities and centrifugal 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 1.7.3.3activity 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
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