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Lysosomal degradation of glycoproteins and glycosaminoglycans. Efflux and recycling of sulphate and N-acetylhexosamines. 1986

L H Rome, and D F Hill

Lysosomal degradation of the carbohydrate portion of glycoproteins and glycosaminoglycans produces monosaccharides and sulphate, which must efflux from the lysosomes before re-entering biosynthetic pathways. We examined the degradation of glycoproteins and glycosaminoglycans by lysosomes isolated from cultured human diploid fibroblasts. Cells were grown for 24 h in medium containing [3H]glucosamine and [35S]sulphate. When lysosomes are isolated from these cells, they contain label primarily in macromolecules (glycoproteins and glycosaminoglycans). Glycoprotein degradation by isolated lysosomes was followed by measuring the release of tritiated sugars from macromolecules and efflux of these sugars from the organelles. Glycosaminoglycan degradation was monitored by the release of both tritiated sugars and [35S]sulphate. During macromolecule degradation, the total amounts of free [35S]sulphate, N-acetyl[3H]glucosamine and N-acetyl[3H]galactosamine found outside the lysosome parallels the amounts of these products released by degradation. The total degradation of glycoproteins and glycosaminoglycans by intact cultured cells was also examined. The lysosomal contribution to degradation was assessed by measuring inhibition by the lysosomotropic amine NH4Cl. After 48 h incubation, inhibition by NH4Cl exceeded 55% of glycoprotein and 72% of glycosaminoglycan degradation. Recycling of [3H]hexosamines and [35S]sulphate by intact cells was estimated by measuring the appearance of 'newly synthesized' radioactively labelled macromolecules in the medium. Sulphate does not appear to be appreciably recycled. N-Acetylglucosamine and N-acetylgalactosamine, on the other hand, are reutilized to a significant extent.

UI MeSH Term Description Entries
D008247 Lysosomes A class of morphologically heterogeneous cytoplasmic particles in animal and plant tissues characterized by their content of hydrolytic enzymes and the structure-linked latency of these enzymes. The intracellular functions of lysosomes depend on their lytic potential. The single unit membrane of the lysosome acts as a barrier between the enzymes enclosed in the lysosome and the external substrate. The activity of the enzymes contained in lysosomes is limited or nil unless the vesicle in which they are enclosed is ruptured or undergoes MEMBRANE FUSION. (From Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed). Autolysosome,Autolysosomes,Lysosome
D002478 Cells, Cultured Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others. Cultured Cells,Cell, Cultured,Cultured Cell
D005347 Fibroblasts Connective tissue cells which secrete an extracellular matrix rich in collagen and other macromolecules. Fibroblast
D006023 Glycoproteins Conjugated protein-carbohydrate compounds including MUCINS; mucoid, and AMYLOID glycoproteins. C-Glycosylated Proteins,Glycosylated Protein,Glycosylated Proteins,N-Glycosylated Proteins,O-Glycosylated Proteins,Glycoprotein,Neoglycoproteins,Protein, Glycosylated,Proteins, C-Glycosylated,Proteins, Glycosylated,Proteins, N-Glycosylated,Proteins, O-Glycosylated
D006025 Glycosaminoglycans Heteropolysaccharides which contain an N-acetylated hexosamine in a characteristic repeating disaccharide unit. The repeating structure of each disaccharide involves alternate 1,4- and 1,3-linkages consisting of either N-acetylglucosamine (see ACETYLGLUCOSAMINE) or N-acetylgalactosamine (see ACETYLGALACTOSAMINE). Glycosaminoglycan,Mucopolysaccharides
D006595 Hexosamines AMINO SUGARS created by adding an amine group to a hexose sugar. Hexosamine
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D013431 Sulfates Inorganic salts of sulfuric acid. Sulfate,Sulfates, Inorganic,Inorganic Sulfates
D046911 Macromolecular Substances Compounds and molecular complexes that consist of very large numbers of atoms and are generally over 500 kDa in size. In biological systems macromolecular substances usually can be visualized using ELECTRON MICROSCOPY and are distinguished from ORGANELLES by the lack of a membrane structure. Macromolecular Complexes,Macromolecular Compounds,Macromolecular Compounds and Complexes,Complexes, Macromolecular,Compounds, Macromolecular,Substances, Macromolecular

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