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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 101 (1974), S. 295-301 
    ISSN: 1432-072X
    Keywords: Chitin Synthase ; Proteinase B ; Saccharomyces cerevisiae ; Morphogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The activity of chitin synthase extracted from whole cells of Saccharomyces cerevisiae shows reproducible changes during the course of batch cultivation. During exponential growth 5–10% of the enzyme occurs in the active form, whereas in the stationary phase no active enzyme can be detected. Of three yeast proteinases, A, B and C, only B is able to activate pre-chitin synthase and inactivate chitin synthase. A new model of the regulation is presented which accounts for the specific location as well as for termination of chitin synthesis during the budding cycle.
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  • 2
    ISSN: 1420-9071
    Keywords: Lysosomes ; lysosomal enzymes ; maturation ; proteinases ; proteolysis ; secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Lysosomal enzymes are subjected to a number of modifications including carbohydrate restructuring and proteolytic maturation. Some of these reactions support lysosomal targeting, others are necessary for activation or keeping the enzyme inactive before being segregated, while still others may be adventitious. The non-segregated fraction of the enzyme is secreted and can be isolated from the medium. It is considered that the secreted lysosomal enzymes fulfill certain physiological and pathophysiological roles. By comparing the secreted and the intracellular enzymes it is possible to distinguish between the reactions that occur before and after the segregation. In this review the reactions that may influence the segregation are referred to as the early processing and those characteristic for the enzymes isolated from lysosomal compartments as the late processing. The early processing is characterized mainly by modifications of carbohydrate side chains. In the late processing, proteolytic fragmentation represents the most conspicuous changes. The review focuses on the compartmentation of the reactions and the proteolytic fragmentation of lysosomal enzyme precursors. While a plethora of proteolytic reactions are involved, our knowledge of the proteinases responsible for the particular maturation reactions remains very limited. The review points also to work with cells from patients affected with lysosomal storage disorders, which contributed to our understanding of the lysosomal apparatus.
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  • 3
    ISSN: 1573-4986
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Lysozyme is an example of an extensively studied secretory enzyme. Glycosylated mutant human lysozyme has been used as a model in studies on the biosynthesis of N-acetyllactosamine repeats in N-linked oligosaccharides. We examined the biosynthesis of the repeats in two doubly glycosylated mutants and describe here a rapid purification and separation of singly and doubly glycosylated molecules. In one of the mutants, the elongation of the repeats is enhanced if the molecules are doubly glycosylated, but not if the carbohydrate is attached to either site individually. This enhancement is not seen in the other doubly glycosylated mutant. Since lysozyme is not structurally related to glycoproteins bearing carbohydrate with N-acetyllactosamine repeats, we propose that in multivalent substrates the synthesis of the repeats can be promoted by a proper spacing of the elongated carbohydrate antennae in addition to any role of the protein backbone.
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  • 4
    ISSN: 1432-0878
    Keywords: Key words: Epididymis ; Efferent ducts ; Cell culture ; Immunocytochemistry ; Immunoprecipitation ; Man
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The way in which the human epididymis modifies spermatozoa during their sojourn in this structure might be clarified by knowledge of the nature of its secretions. We have examined the presence of several lysosomal hydrolases in human epididymal tissue and fluids, and their synthesis and secretion by monolayer cultures. Tissues were obtained from men undergoing orchidectomy for prostatic carcinoma. The enzymes cathepsin D and acid α-glucosidase were localised in the lysosomes of epithelial cells from the corpus epididymidis, by an immunocytochemical technique. Cathepsin D was also found in epithelial cells of the efferent ducts within lysosomes, apical vesicles and multivesicular bodies. No immunolocalisation of acid glucosidase in the efferent ducts or on the microvilli of the corpus was demonstrable. Cathepsin D, β-hexosaminidase (N-acetylglucosaminidase) and α-glucosidase were measurable in the luminal fluid from the human corpus epididymidis; β-hexosaminidase was secreted into the culture medium by confluent monolayers of epididymal and efferent duct cells. Immunoprecipitation of cell extracts and culture medium of these cultures incubated with 35S-methionine revealed that the precursors of cathepsin D and β-hexosaminidase were synthesized and secreted by such monolayers. Thus, active lytic enzymes are secreted by the human epididymis and could modify sperm membranes.
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  • 5
    ISSN: 1432-0878
    Keywords: Key words: Lysosomal membrane antigen ; Immunohistochemistry ; Biosynthesis ; Prostate-membrane-specific antigen ; Apocrine secretion ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The tissue distribution, preferentially in the human male genital system, and the subcellular localization of the lysosome-associated membrane protein 2 (lamp 2) was studied immunohistochemically using a mouse monoclonal antibody, 2D5. Strong immunoreactivity was present in the tubular system of the kidney, in acinar cells of salivary glands and pancreas, prostate, mammary glands, placenta and in cutaneous sweat glands. Moderate immunoreactivity was observed in cerebral neuronal cells, epidermal cells, testis, epididymis, seminal vesicle and endometrium. Very low immunoreactivity was found in liver. In some of the tissues mentioned, the distribution pattern of immunoreactivity is smooth and homogeneous, while in others it is granular and concentrated in the supra- or perinuclear cytoplasm. The subcellular distribution was studied on ultracryosections and on pre-embedding-processed chopper sections of human prostate. In the latter gland, the protein is not restricted to epithelium, but is also present in stromal cells. Ultrastructurally, the immunoreactivity in secretory cells was localized in electron-translucent vacuoles and granules, including the secretory granules. A close association with cell membranes was not generally the case. Only part of the immunoreactive material was linked to the apical plasma membrane pointing to a biosynthesis independent from an association step with the apical plasma membrane. As shown by immunoelectron microscopy and Western blotting, a high amount of lamp 2 is secreted and is found in so-called prostasomes. The findings indicate that in the human prostate most of the membrane-bound lamp 2 is released from the secretory cells, presumably in an apocrine fashion.
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  • 6
    ISSN: 1432-0878
    Keywords: Key words Procathepsin D ; Lysosomes ; Endocytosis ; Baby hamster kidney (BHK) cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  BHK cells transfected with human cathepsin D (CD) cDNA normally segregate the autologous hamster cathepsin D while secreting a large proportion of the human proenzyme. In the present work, we have utilized these transfectants to examine to what extent the mannose-6-phosphate-dependent pathway for lysosomal enzyme segregation contributes to the differential sorting of human and hamster CD. We report that, in recipient control BHK cells, the rate of mannose-6-phosphate-dependent endocytosis of human procathepsin D secreted by transfected BHK cells is lower than that of hamster procathepsin D and much lower than that of human arylsulphatase A. The missorted human enzyme bears phosphorylated oligosaccharides and most of its phosphate residues are “uncovered”, like the autologous enzyme. Thus, despite both the Golgi-associated modifications of oligosaccharides, i.e. the phosphorylation of mannose and the uncovering of mannose-6-phosphate residues, which proceed on human and hamster procathepsin D with comparable efficiency, only the latter is accurately packaged into lysosomes. Ammonium chloride partially affects the lysosomal targeting of cathepsin D in control BHK cells, whereas in transfected cells, this drug strongly inhibits the maturation of human procathepsin D and slightly enhances its secretion. These data indicate that: (1) over-expression of a lysosomal protein does not saturate the Golgi-associated reactions leading to the synthesis of mannose-6-phosphate; (2) a portion of cathepsin D is targeted independently of mannose-6-phosphate receptors in the transfected BHK cells; and (3) whichever mechanism for lysosomal delivery of autologous procathepsin D is involved, this is not saturated by the high rate of expression of human cathepsin D.
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  • 7
    ISSN: 1432-0878
    Keywords: Epididymis ; Efferent ducts ; Cell culture ; Immunocytochemistry ; Immunoprecipitation ; Man
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The way in which the human epididymis modifies spermatozoa during their sojourn in this structure might be clarified by knowledge of the nature of its secretions. We have examined the presence of several lysosomal hydrolases in human epididymal tissue and fluids, and their synthesis and secretion by monolayer cultures. Tissues were obtained from men undergoing orchidectomy for prostatic carcinoma. The enzymes cathepsin D and acid α-glucosidase were localised in the lysosomes of epithelial cells from the corpus epididymidis, by an immunocytochemical technique. Cathepsin D was also found in epithelial cells of the efferent ducts within lysosomes, apical vesicles and multivesicular bodies. No immunolocalisation of acid glucosidase in the efferent ducts or on the microvilli of the corpus was demonstrable. Cathepsin D, β-hexosaminidase (N-acetylglucosaminidase) and α-glucosidase were measurable in the luminal fluid from the human corpus epididymidis; β-hexosaminidase was secreted into the culture medium by confluent monolayers of epididymal and efferent duct cells. Immunoprecipitation of cell extracts and culture medium of these cultures incubated with 35S-methionine revealed that the precursors of cathepsin D and β-hexosaminidase were synthesized and secreted by such monolayers. Thus, active lytic enzymes are secreted by the human epididymis and could modify sperm membranes.
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  • 8
    ISSN: 1572-9699
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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