Biosynthesis of two lysosomal enzymes in macrophages. Evidence for a precursor of beta-galactosidase.
We have purified beta-galactosidase and beta-glucuronidase from macrophages of thioglycollate-treated mice using concanavalin A chromatography and immunoprecipitation. The apparent molecular weight of the beta-galactosidase subunit, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, changed during a long term pulse-chase experiment. Following a 1-h pulse with [3H]leucine, radiolabel was present exclusively in an Mr = 82,000 form. However, after a 3-h chase in medium containing unlabeled leucine, most label migrated at Mr = 63,000, and at 24 h, all label was in the Mr = 63,000 form. Electrophoresis of peptides produced by cyanogen bromide cleavage of immunoprecipitates demonstrated structural similarities between precursor and mature forms. A mutation in the mouse, which is known to depress the rate of synthesis of beta-galactosidase in many cell types, proportionately decreased incorporation of [3H]leucine into both the Mr = 82,000 and 63,000 forms. Therefore, by kinetic, structural, and genetic evidence, the large molecular weight beta-galactosidase is a precursor of mature macrophage enzyme. No precursor of the Mr = 75,000 subunit of beta-glucuronidase was detected.
D000818:Animals; D004792:Enzyme Precursors / Q000096:biosynthesis*; D005260:Female; D005696:Galactosidases / Q000096:biosynthesis*; D005966:Glucuronidase / Q000096:biosynthesis*; D007700:Kinetics; D008247:Lysosomes / Q000201:enzymology*; D046911:Macromolecular Substances; D008264:Macrophages / Q000201:enzymology*; D051379:Mice; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D014176:Protein Biosynthesis; D001616:beta-Galactosidase / Q000096:biosynthesis*
D004792:Enzyme Precursors; D046911:Macromolecular Substances; D010446:Peptide Fragments; D005696:Galactosidases; D001616:beta-Galactosidase; D005966:Glucuronidase