Immature precursor catalase in subcellular fractions of rat liver

Dialysis of the peroxisomal extract, microsomal extract and cytosol fraction of rat liver against a solution containing 44 mM acetate buffer, pH 4.1, and 22% ethanol resulted in elimination of immature and enzymatically inactive catalase as insoluble precipitates, leaving mature and active catalase in solution. These catalase molecules in the three different subcellular compartments were doubly labeled with injected radioactive amino acids, for 30 min with [3H]leucine and for 90 min with [14C]leucine. The specific radioactivities of peroxisomal catalase remained unchanged upon the dialysis described above. This was also the case with microsomal catalase, however, the values were much higher than those of peroxisomal catalase. On the other hand, cytosol catalase showed remarkably decreased radioactivities after the dialysis, which were comparable to those of peroxisomal catalase, and the immature and inactive catalase which had been removed by this treatment was estimated to be as highly radioactive as the microsomal catalase. By affinity chromatography using anticatalase antibody both the microsomal extract and cytosol fraction were found to contain enzymatically inactive and probably immature catalase, which did not occur in peroxisomal extracts. However, when examined by SDS-polyacrylamide gel electrophoresis, the catalases in the three different subcellular fractions gave identical single bands corresponding to the monomer subunit of this enzyme protein, and no other larger molecule was detected. It was also found that the peroxisomal mature catalase did not migrate in polyacrylamide gel electrophoresis the same as that in microsomes and in cytosol, the latter two exhibiting the same mobility. Based on these results and others previously obtained, intracellular events in the maturation and transfer of newly synthesized catalase are discussed.