Characterization of enzymes and glycoproteins in rat liver lysosomal membranes

A simple method for the preparation of lysosomes from livers of rats injected with Triton WR 1339 was developed. Enzymic characterization showed that the Triton WR 1339-filled lysosome (tritosome) preparation isolated by this procedure was almost completely free from mitochondria, peroxisomes, and microsomes. With this method, tritosomes were purified about 50 times with a yield of 8%. The tritosomal membrane fraction was prepared by osmotic disruption of the purified tritosomes followed by washing with 1 M NaCl. Analysis by SDS-polyacrylamide gel electrophoresis showed that tritosomal membrane proteins were distinct from those of plasma membranes. The major glycoproteins found in tritosomal membranes in the higher molecular weight region were not detected in plasma membranes. When livers were labeled with L-[3H]leucine or D-[3H]glucosamine, the incorporation of both isotopes into tritosomes attained the maximum value at around 3 h after the isotope injection. Radioactivities associated with the tritosomal membranes decayed slower than those of the tritosomal contents. SDS-polyacrylamide gel electrophoresis of the membranes labeled with the isotopes for various times demonstrated the distribution and variation with time of radioactivity in the protein and glycoprotein components. The results indicate that the turnover rate of the protein and glycoprotein components in the tritosomal membrane is heterogeneous.