Coated vesicles from rat liver and calf brain contain lysosomal enzymes bound to mannose 6-phosphate receptors

Abstract

Coated vesicles from calf brain and rat liver contain cryptic receptors which recognize and bind lysosomal enzymes via mannose 6-phosphate residues on oligosaccharide side chains (Campbell, C. H., Fine, R. E., Squicciarini, J., and Rome, L. H. (1983) J. Biol. Chem. 258, 2628-2633). In addition to mannose 6-phosphate receptors, we now report that coated vesicles from calf brain and rat liver contain the lysosomal enzymes alpha-L-fucosidase, beta-galactosidase, beta-glucosidase, beta-hexosaminidase, alpha-L-iduronidase, and alpha-mannosidase. Enzyme activities co-migrated with coated vesicles purified by agarose gel electrophoresis. Treatment of intact coated vesicles with pronase (0.05 mg/ml) had little effect on lysosomal enzyme activities, whereas a similar treatment of coated vesicles in the presence of 0.045% taurodeoxycholate resulted in the loss of most of the enzyme activities. Addition of 10 mM mannose 6-phosphate to disrupted liver coated vesicles specifically displaced up to 80% of the cryptic lysosomal enzyme activity. Disrupted liver coated vesicles and highly purified liver lysosomes were treated with anti-beta-hexosaminidase A and anti-beta-galactosidase antibodies and immunoprecipitates were analyzed by polyacrylamide gel electrophoresis. High molecular weight bands were present in the coated vesicle immunoprecipitates which were not present in the lysosome immunoprecipitates. The data suggest that coated vesicles contain mannose 6-phosphate receptor-bound lysosomal enzymes, some of which are of a higher molecular weight form. These higher molecular weight forms may represent newly synthesized enzymes that are en route to lysosomes.