POSTTRANSLATIONAL IMPORT OF 3-KETOACYL-COA THIOLASE INTO RAT-LIVER PEROXISOMES IN-VITRO

Cell-free translation products of hepatic free polysomal RNA from a cl ofibrate-treated rat were incubated at 26 degrees C for 0-60 min with a post-heavy mitochondrial supernatant fraction from normal rat liver. Exogenously added proteinase K-resistant precursor and mature forms o f peroxisomal 3-ketoacyl-CoA thiolase were recovered in a particulate fraction and increased with time. Both forms of thiolase cosedimented with peroxisomes, when the proteinase K-treated import reaction mixtur e was centrifuged in a sucrose density gradient. The in vitro import a nd processing of thiolase precursors, types A and B, was likewise repr oduced with highly purified peroxisomes. These results strongly sugges t that the precursor form of 3-ketoacyl-CoA thiolase is translocated i nto peroxisomes, apparently without tight coupling with proteolytic pr ocessing to the mature protein.