Biosynthesis of peroxisomal enzymes in the methylotrophic yeast Hansenula polymorpha

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Abstract
The dramatic expansion of the peroxisomal compartment known to occur in the methanol-utilizing yeast H. polymorpha on transfer from glucose- to methanol-containing media is accompanied by the synthesis of at least 6 major polypeptides that dominate the polypeptide pattern of total cell extracts analyzed by NaDodSO4[sodium dodecyl sulfate]/polyacrylamide gel electrophoresis. Two of these polypeptides were identified by immunochemical methods as the monomers of the peroxisomal enzymes alcohol oxidase and catalase. The biosynthesis of these 2 peroxisomal enzymes was studied by in vitro translation and in vivo labeling experiments. By the criterion of mobility in NaDodSO4/polyacrylamide gel electrophoresis, the in vitro- and in vivo-synthesized monomers were indistinguishable from each other, both in the case of alcohol oxidase and in that of catalase. Thus, neither of these peroxisomal enzymes apparently are synthesized as larger precursors. However, further analysis of in vitro-synthesized vs. mature peroxisomal alcohol oxidase showed that the in vitro-synthesized form sedimented as a 5S monomer and not, like the mature peroxisomal enzyme, as a 20S octamer. Moreover, the in vitro-synthesized form was highly susceptible to trypsin digestion whereas the mature 20S octamer apparently was resistant.