Biogenesis of peroxisomes: intracellular site of synthesis of catalase and uricase.

Abstract

The intracellular site of synthesis of 2 peroxisomal enzymes of rat liver, uricase (urate:oxygen oxidoreductase, EC 1.7.3.3) and catalase (hydrogen peroxide:hydrogen peroxide oxidoreductase, EC 1.11.1.6), was localized on free ribosomes and not membrane-bound ribosomes. Free polysomes and membrane-bound polysomes, prepared by classical cell fractionation techniques from rat liver, were incubated for protein synthesis in a cell-free system derived from rabbit reticulocytes. Characterization of the total translation products by polyacrylamide gel electrophoresis in sodium dodecyl sulfate, as well as by immunoprecipitation with anti-rat albumin antiserum, confirmed that good separation of the 2 polysome classes was achieved. Uricase and catalase were immunoprecipitable from translation products directed by free polysomes or phenol-extracted free polysomal mRNA but not from products of membrane-bound polysomes. Furthermore, unlike albumin, nascent uricase and catalase were not cotranslationally segregated by dog pancreas microsomal membranes. Uricase and catalase are probably transferred to the interior of peroxisomes by a post-translational mechanism; an hypothesis is formulated here for the biogenesis of peroxisomes.