Secondary lysosome

A problem with employment of ASON in a larger clinical setting is their poor uptake and inappropriate intracellular compartmentalization, e.g., sequestration in endosomal or lysosomal complexes. In addition, there is a need for a very careful selection of the ASON-mRNA pair sequences that would most efficiently hybridize. To date, several computer programs are used to predict the secondary and tertiary structures of the target mRNA and, in turn, which of the mRNA sequences are most accessible to the ASON. However, even with this sophisticated techniques, the choice of base-pairing partners still usually includes a component of empiricism. Despite these principal limitations, it has become clear that ASON can penetrate into cells and mediate their specific inhibitory effect of the protein synthesis in various circumstances. 

As an example, the low-density lipoprotein (LDL) molecule and its receptor (Chapter 25) are internalized by means of coated pits containing the LDL receptor. These endocytotic vesicles containing LDL and its receptor fuse to lysosomes in the cell. The receptor is released and recycled back to the cell surface membrane, but the apoprotein of LDL is degraded and the choles-teryl esters metabolized. Synthesis of the LDL receptor is regulated by secondary or tertiary consequences of pinocytosis, eg, by metabolic products—such as choles-... 

FIGURE 1-6 A portion of a Golgi apparatus. The smooth-mem-braned cisternae appear beaded. The many circular profiles represent tangentially sectioned fenestrations and alveolate vesicles (primary lysosomes). Two of the latter can be seen budding from Golgi saccules (arrows). Mitochondria and a dense body (secondary lysosomes) are also present. x60,000. 

Multivesicular bodies are usually found in association with the Golgi apparatus and are visualized by EM as small, single membrane-bound sacs approximately 0.5 Jim in diameter. They contain several minute, spherical profiles, sometimes arranged about the periphery. They are believed to belong to the lysosome series prior to secondary lysosomes because they contain acid hydrolases and apparently are derived from primary lysosomes. 

Vacuoles (70-78) are membrane-bound regions of the cell filled with cell sap. Vacuoles are surrounded by a tonoplast (vacuolar membranes) and are diverse with distinct functions. Most investigators believe that lysosomes and the plant vacuoles are the same. Vacuoles develop turgor pressure and maintain tissue rigidity. They are storage components for various metabolites such as reserve proteins in seeds and malic acid in crassulacean acid metabolism (CAM) plants. Vacuoles canremove toxic secondary products and are the sites of pigment deposition. 

The morphological alterations induced by aminoglycosides in LLC-PKi cells correlated well with in vivo histological findings in the kidney, including the formation of secondary lysosomal inclusions referred to as myeloid bodies. 

Fig. 11.2 (a) HAADF-STEM image of a stained cell section (40nm thick). A SWNT cluster within a lysosome invading the lysosomal cell membrane, (b) Corresponding high-resolution lattice image of SWNTs at the lysosomal membrane from boxed area. Cytoplasm (cy) and secondary... 

Fig. 11.6 A series of horizontal (b-c) slices and vertical slices (e-h) through a HAADF-STEM reconstruction of a freeze-dried whole cell exposed to C60 for 24 h. Slices are 0.15 im apart, (a) Voltex reconstruction of the same cell showing a horizontal orthoslice through the 3-D reconstruction. (d) Vertical orthoslice through the Voltex reconstruction. Slices through the reconstruction illustrate membranes (m), the nucleus (n), the cytoplasm (c), and secondary lysosomes (1). Several distributions of particles with the cell are revealed at each height through the reconstructed cell (See Color Plates)...

As discussed above, ufa, which are present primarily in cellular membranes, appear to be particularly susceptible to oxidative degradation by ozone. Various studies of membrane lipid peroxidation have implicated this process in damage to organelles, including mitochondria, micro-somes, and lysosomes, as well as to the cell membrane itself. By analogy, it is conceivable that many of the findings in cells and subcellular components described in other sections of this chapter are secondary to ozone-induced lipid peroxidation. However, this remains conjectural. 

Fig. I. Endocytic pathways used by cells to internalize soluble macromolecules [25] fluid-phase pinocytosis (1), adsorptive pinocytosis (2), and receptor-mediated endocytosis (pinocytosis) (6). Each of these processes involves a formation of a sealed vesicle formed from the plasma membrane which encloses part of the extracellular medium. The internalization of a polymer-drug conjugate (P-D), and targeted polymer-drug conjugate ( => —P-D) is shown. Other abbreviations — = cell surface receptor/antigen 1 = clathrin molecule X = lysosomal enzyme. Fluid-phase pinocytosis (1) and adsorptive pinocytosis (2) are nonspecific processes which direct the macromolecule into the lysosomal compartment of the cell. Once P-D is internalized, whether by (1) or (2), the resulting endosome (3) is ultimately fused with a primary lysosome (4) forming a secondary lysosome (5). In the latter compartment P-D is in contact with several types of lysosomal enzymes. The membrane of (5) is impermeable to macromolecules. Consequently, the structure of P-D may be designed in such...

The major secondary events are changes in membrane structure and permeability, changes in the cytoskeleton, mitochondrial damage, depletion of ATP and other cofactors, changes in Ca2+ concentration, DNA damage and poly ADP-ribosylation, lysosomal destabilization, stimulation of apoptosis, and damage to the endoplasmic reticulum. 

Secondary events result from primary events, for example, changes in membrane structure/permeability, mitochondrial damage, and lysosomal destabilization. Tertiary events are final observable manifestations, for example, fatty change and phospholipidosis, apoptosis, blebbing, and necrosis. 

Reiter et al. (43) have shown that a second enzyme can also act to degrade SGG. They found that secondary lysosomes from rat liver contained not only arylsulfatase A, but also a lipase activity that could act to de-acylate SGG. Under the conditions used, more product was formed by the action of the lipase on SGG than by the action of arylsulfatase A. These workers also found that the latter enzyme could use the lyso-SGG as a substrate. It would be... 

Mucus turnover rate. The turnover rate of the mucus layer is another physiological factor that affects mucoadhesion. Mucus turnover limits the potential duration of adhesion at the desired site of application. Within the GI tract, mucus is lost continuously secondary to enzymatic degradation (pepsin, lysosomal enzymes, and pancreatic enzymes), acid... 

Tabuchi N., Akasaki K. and Tsuji H. (2000) Two acidic amino acid residues, Asp(470) and Glu(471), contained in the carboxyl cytoplasmic tail of a major lysosomal membrane protein, LGP85/LIMP II, are important for its accumulation in secondary lysosomes. Biochem. Biophys. Res. Commun. 270, 557-563. 

B-100,E receptors have now been purified. They are glycoproteins, synthesized as a precursor of Mr 120,000 (T8), then converted to the mature protein of Mr 164,000 (S14) and inserted into the plasma membrane of cells. Human fibroblasts contain up to about 20,000 such receptors per cell, depending on cellular cholesterol requirements. It is thought that at any one time less than 1% of such receptors are newly synthesized, and that most have already been internalized by the cell and have then been recycled back to the surface. Once bound to the receptor, LDL is rapidly internalized (half-time less than 10 minutes). The ligand-receptor complex moves to particular areas on the surface of the cell, coated pits, where internalization occurs as the coated pit invaginates to form an endocytic vesicle (G15). The endocytic vesicle migrates through the cytoplasm until it fuses with a primary lysosome to form a secondary lysosome. 

The invaginated membrane then pinches off to form detached vesicles. The pinocytic vesicles (endosomes) migrate inwardly and fuse with lysosomes, which contain many lyosomal enzymes, to form secondary lyosomes. The ligand is degraded by the lysosomal enzymes, the degraded products are released and the membrane is recycled back to the plasma membrane. Alternatively, the secondary lysosomes can fuse with the cell membrane, leading to exocytosis of their contents, and the membranes are recycled back to the plasma membrane. 

Prenatal diagnosis of I-cell disease has been based on greatly reduced phosphotransferase activity (cf. Biochemical Perspectives section) and abnormal intracellular-extracellular distribution of lysosomal enzymes in cultured amni-otic fluid cells (Table 17-3).As indicated in Table 17-3, amniotic fluid cells secrete large amounts of lysosomal enzymes into the extracellular medium. Decreased levels of lysosomal enzymes in chorionic villi obtained by biopsy have also been observed in I-cell disease however, the characteristic secondary effect (i.e.,increased levels of lysosomal enzymes in the extracellular compartment) is only partially expressed or not expressed at all in chorionic villi, suggesting an alternative mechanism for the transport of lysosomal proteins. Although... 

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