Biosynthesis and transport of lysosomal enzymes in human monocytes and macrophages. Effects of ammonium chloride, zymosan and tunicamycin

Abstract

Human monocytes and macrophages synthesize lysosomal enzymes as larger precursors. The polypeptide patterns of several lysosomal-enzyme precursors and their mature forms are similar to those observed in human fibroblasts. Like fibroblasts, the monocytes and macrophages release small amounts of lysosomal-enzyme precursors. The lysosomotropic NH4+ cation enhances this release. In contrast, zymosan, a degranulating agent, causes release of both the mature and the precursor forms of the lysosomal enzymes. Both NH4Cl and zymosan inhibit maturation of the precursors. The fractional amounts of mature cathepsin D and beta-hexosaminidase released in the presence of zymosan are strikingly different. Probably, in the macrophages several lysosomal organelles are packaged with different relative contents of lysosomal enzymes. The transport of the precursors of cathepsin D into lysosomes is inhibited by tunicamycin. Therefore oligosaccharide side chains are likely to function as signals in packaging of lysosomal enzymes in macrophages also.