Immunocytochemical localization of catalase in rat liver.

The intracellular localization of catalase has been studied using monospecific Fab fragments against rat liver catalase (RLC) and preembedding immunoelectron microscopy. Purified RLC, exhibiting a single band on sodium dodecyl sulfate gel electrophoresis, was used for the immunization of rabbits. The anti-RLC IgG was purified by affinity chromatography. Fab fragments were obtained by papain digestion and were labeled with horseradish peroxidase (HRP) using a modified two-step procedure and glutaraldehyde as coupling agents. Livers were perfused with 4% depolymerized paraformaldehyde and chopper sections were incubated with HRP-labeled Fab fragments against RLC. Because of the limited penetration of labeled Fab fragments into chopper sections a simple method for preparation of a cell suspension from aldehyde-fixed livers was devised. Adequate staining of more than 90% of cell was obtained by incubation of cell suspensions for 12--18 hr with the labeled antibody. By light microscopy specific staining was present in fine granules in the cytoplasm of hepatocytes. By electron microscopy the electron-dense reaction product was localized in the matrix of peroxisomes with no reaction in the endoplasmic reticulum and the Golgi complex. In some hepatocytes, positively reacted peroxisomes were seen side by side with unstained particles. Although focal diffusion was noted around a few peroxisomes, no evidence of cytoplasmic catalase independent of peroxisomes was found. These observations indicate that in rat liver peroxisomes are the only organelle containing substantial amounts of catalase antigen and rule out any involvement of the endoplasmic reticulum and the Golgi complex in the sequestration of this protein.