Studies on rat liver catalase. XI. Site of synthesis and segregation by stripped ER membranes.

We reinvestigated the site of synthesis of rat liver catalase, and it has been reconfirmed that catalase is synthesized not only by free polysomes but also by membrane-bound polysomes. Considerable amounts of nascent catalase on rough microsomes were released from the membrane into the medium upon incubation with puromycin, not transported directly into the intracisternal cavity of microsomes. On the other hand, catalase newly synthesized in vitro was shown to be segregated by stripped rat liver microsomal membranes in a state resistant to proteolysis. Since this segregation occurred without coupled protein synthesis, catalase appears to be transported by a mechanism different from co-translational transfer. A hypothesis is presented regarding the mechanism of intracellular transport of liver catalase.