| 3. |
- Barros, Raúl J., et al.
(författare)
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Physical characterization of porous materials and correlation with the activity of immobilized enzyme in organic medium
- 1998
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 16:1, s. 67-85
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Tidskriftsartikel (refereegranskat)abstract
- A series of commonly used porous supports was characterized by determination of particle size distribution, porosity, surface area (total and distributions with pore diameters) and skeletal density. The performance of immobilized α-chymotrypsin catalyzed dipeptide synthesis in an acetonitrile medium was correlated with these physical properties.At high enzyme loading, when internal mass transfer limitations are expected to occur, the activity can be correlated with the support characteristic parameter. This is a combination of physical properties such as particle size, porosity, and volumetric porosity, which influence the substrate diffusion rate. At low enzyme loading the important parameter is the accessible surface area, which will determine how the enzyme is distributed in the pores of the support. When assessing the effect of the support material on enzymatic activity, the geometric considerations studied here should always be contemplated before making any assumptions about direct effects of support material on enzymatic catalytic properties.
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| 5. |
- Zimmerli, Stefan, et al.
(författare)
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Phagosome-Lysosome Fusion Is a Calcium-independent Event in Macrophages
- 1996
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Ingår i: Journal of Cell Biology. - : Rockefeller University Press. - 0021-9525 .- 1540-8140. ; 132:1-2, s. 49-61
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Tidskriftsartikel (refereegranskat)abstract
- Phagosome-lysosome membrane fusion is a highly regulated event that is essential for intracellular killing of microorganisms, Functionally, it represents a form of polarized regulated secretion, which is classically dependent on increases in intracellular ionized calcium ([Ca2+](i)). Indeed, increases in [Ca2+](i) are essential for phagosome-granule (lysosome) fusion in neutrophils and for lysosomal fusion events that mediate host cell invasion by Trypanosoma cruzi trypomastigotes, Since several intracellular pathogens survive in macrophage phagosomes that do not fuse with lysosomes, we examined the regulation of phagosome-lysosome fusion in macrophages. Macrophages (MO) were treated with 12.5 mu M bis-(2-amino-S-methylphenoxy) ethane-N,N,N',N',-tetraacetic acid tetraacetoxymethyl ester (MAPT/AM), a cell-permeant calcium chelator which reduced resting cytoplasmic [Ca2+]; from 80 nM to less than or equal to 20 nM and completely blocked increases in [Ca2+](i) in response to multiple stimuli, even in the presence of extracellular calcium, Subsequently, MO phagocytosed serum-opsonized zymosan, staphylococci, or Mycobacterium bovis, Microbes were enumerated by 4',6-diamidino-2-phenylindole, dihydrochloride (DAPI) staining, and phagosome-lysosome fusion was scored using both lysosome-associated membrane protein (LAMP-1) as a membrane marker and rhodamine dextran as a content marker for lysosomes, Confirmation of phagosomelysosome fusion by electron microscopy validated the fluorescence microscopy findings, We found that phagosome-lysosome fusion in MO occurs normally at very low [Ca2+](i) (less than or equal to 20 nM), Kinetic analysis showed that in MO none of the steps leading from particle binding to eventual phagosome-lysosome fusion are regulated by [Ca2+](i) in a rate-limiting way. Furthermore, confocal microscopy revealed no difference in the intensity of LAMP-1 immunofluorescence in phagolysosome membranes in calcium-buffered vs, control macrophages, We conclude that neither membrane recognition nor fusion events in the phagosomal pathway in macrophages are dependent on or regulated by calcium.
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