Peptide mapping of peroxisomal catalase and its precursor. Comparison to the primary wheat germ translation product

To investigate possible structural modifications of catalase during its biogenesis and packaging into peroxisomes, we have labeled three species of catalase with [35S]methionine: the wheat germ cell-free translation product, the extraperoxisomal precursor made in vivo in rat liver, and mature peroxisomal catalase. These three species have identical mobilities in sodium dodecyl sulfate polyacrylamide gels, when analyzed separately or in mixtures. Tryptic digestion yields 10 [35S]Met-labeled peptides from each, which are indistinguishable when mapped in two dimensions by electrophoresis and chromatography. Partial proteolyses of the three species in sodium dodecyl sulfate gels yielded identical fragmentation patterns. The primary translation product of catalase was labeled with formyl[35S] methionine; its size was indistinguishable from the subunit of mature catalase. Its radioactivity appeared in dansyl methionine if and only if it was deformylated prior to dansylation. These results demonstrate that within the limits of the methods, catalase undergoes no covalent modification during its uptake into peroxisomes and its subsequent maturation to a tetrameric hemoprotein.