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891.
892.
Miguel Arroyo José María Sánchez-Montero José Vicente Sinisterra 《Biotechnology Techniques》1996,10(4):263-266
Summary We describe a qualitative method to predict the pre-equilibration aw, system value in which, covalent immobilized lipase B from Candida antarctica to sepharose and silica, displayed best synthetic activity. The methodology is based in the analysis of the water adsorption isotherms of the biocatalyst in air and in the organic solvent. The biocatalyst is active at pre-equilibration aw values higher than the divergence point between both isotherms. In addition, native and immobilized lipase display highest activity if the biocatalyst is pre-equilibrated at aw=P point. For preparative purposes, the validity of the method was proved in the esterification of racemic 2-(4-isobutyl phenyl) propionic acid with 1-propanol in isooctane at long reaction time. 相似文献
893.
Summary The Castellani's Method for the preservation of Sclerotium rolfsii in sterile distilled water was tested. Culturing on Potato Dextrose Yeast extract (PDY) slants, the current system used, was also evaluated. Preservation of sclerotia according to the Castellani's method allowed the strain survival for more than two years. Comparing with the strain periodically activated, a critical decrease (about 80%) in -glucan synthesizing capacity was detected for mycelium preserved either on PDY slants or in water. Activation of stored sclerotia followed by subculturing in liquid Production Medium (PM) allowed preparation of homogeneous suspensions for batch fermentations, and scleroglucan concentrations achieved were similar to those with the strain periodically activated. 相似文献
894.
Bruce Aylward Katie Allen Jaime Echeverría Joseph Tosi 《Biodiversity and Conservation》1996,5(3):315-343
The paper discusses the sustainability of the Monteverde Cloud Forest Preserve in the context of Costa Rican ecotourism. While the history of the Preserve is somewhat unique, the analysis of visitation, financial, ecological and economic factors provides a convincing case that tourism at the Preserve is sustainable. The experience of the Preserve is also put in the context of Costa Rican ecotourism, particularly to the national parks. The paper concludes that the Preserve has played a very important role in the development of Costa Rica as an ecotourism destination. Nonetheless, the failure of experience at the Preserve to inform recent changes in national park pricing policy reveal that Costa Rica has yet to fully capitalize on the experience gained and lessons learned at the Preserve. 相似文献
895.
896.
Ligand binding to heparan sulfate proteoglycans induces their aggregation and distribution along actin cytoskeleton. 总被引:1,自引:1,他引:0 下载免费PDF全文
R G Martinho S Castel J Urea M Fernndez-Borja R Makiya G Olivecrona M Reina A Alonso S Vilar 《Molecular biology of the cell》1996,7(11):1771-1788
Cell surface heparan sulfate proteoglycans (HSPGs) participate in molecular events that regulate cell adhesion, migration, and proliferation. The present study demonstrates that soluble heparin-binding proteins or cross-linking antibodies induce the aggregation of cell surface HSPGs and their distribution along underlying actin filaments. Immunofluorescence and confocal microscopy and immunogold and electron microscopy indicate that, in the absence of ligands, HSPGs are irregularly distributed on the fibroblast cell surface, without any apparent codistribution with the actin cytoskeleton. In the presence of ligand (lipoprotein lipase) or antibodies against heparan sulfate, HSPGs aggregate and colocalize with the actin cytoskeleton. Triton X-100 extraction and immunoelectron microscopy have demonstrated that in this condition HSPGs were clustered and associated with the actin filaments. Crosslinking experiments that use biotinylated lipoprotein lipase have revealed three major proteoglycans as binding sites at the fibroblast cell surface. These cross-linked proteoglycans appeared in the Triton X-100 insoluble fraction. Platinum/carbon replicas of the fibroblast surface incubated either with lipoprotein lipase or antiheparan sulfate showed large aggregates of HSPGs regularly distributed along cytoplasmic fibers. Quantification of the spacing between HSPGs by confocal microscopy confirmed that the nonrandom distribution of HSPG aggregates along the actin cytoskeleton was induced by ligand binding. When cells were incubated either with lipoprotein lipase or antibodies against heparan sulfate, the distance between immunofluorescence spots was uniform. In contrast, the spacing between HSPGs on fixed cells not incubated with ligand was more variable. This highly organized spatial relationship between actin and proteoglycans suggests that cortical actin filaments could organize the molecular machinery involved in signal transduction and molecular movements on the cell surface that are triggered by heparin-binding proteins. 相似文献
897.
898.
Summary Growing hyphal tips of higher fungi contain an organized assemblage of secretory vesicles and other cell components collectively known as the Spitzenkörper. Until now, the Spitzenkörper has been portrayed as a single spheroid complex located near the apical cell wall. This study demonstrates the occurrence of multiple Spitzenkörper in growing hyphal apices imaged by video-enhanced phase-contrast microscopy. In addition to the main Spitzenkörper, smaller satellite Spitzenkörper arise a few micrometers behind the apical pole. Four developmental stages were identified: (a) the satellites first appeared as faint phase-dark plaques next to the plasma membrane, (b) gradually increased in size and assumed an ovoid profile, (c) they migrated to the hyphal apex, and (d) finally they merged with the main Spitzenkörper. After the merger, the main Spitzenkörper temporarily increased in size. Satellites were observed in 14 fungi, most of which had relatively large (5–10 m diam.), fast-growing hyphae (2–33 m/min elongation rate). The average frequency of in-focus satellites was 7+/min forFusarium culmorum and 11+/min forTrichoderma viride. As with the main Spitzenkörper, satellites were present only in growing cells. They were transient and remained visible for 3–8 s before merging with the main Spitzenkörper. Within the hyphae, satellites travelled up to six times faster than the average cell elongation rate. Multiple satellites sometimes occurred simultaneously; up to three were seen within a hyphal apex at the same time. Localized cell enlargement occurred next to stationary satellites, suggesting that satellite Spitzenkörper are functional as sources of new cell surface before they reach the main Spitzenkörper; therefore, they account for some variations in the profiles of the growing hyphae. By electron microscopy, satellites consisted of small clusters of apical vesicles surrounding a group of microvesicles located next to the plasma membrane. The identification and behavior of the satellites represent clear evidence of directional mass transport of vesicles toward the hyphal apex. Our observations indicate that satellites are a common phenomenon in growing hyphal apices of septate fungi and that they contribute to growth of the hyphal apex.Abbreviations VSC
vesicle supply center 相似文献
899.
900.
J. C. Rodríguez-Aguilera F. Navarro A. Arroyo F. J. Alcaín J. M. Villalba P. Navas 《Protoplasma》1995,184(1-4):229-232
Summary Ascorbate is stabilized in the presence of HL-60 cells. Our results showed that cAMP derivatives and agents that increase cAMP stimulate the ability of HL-60 cells to stabilize ascorbate. On the other hand, tunicamycin, a glycosilation-interfering agent, inhibited this ability. The ascorbate stabilization in the presence of HL-60 cells has been questioned as a simple chemical effect. Further properties and controls about the enzymatic nature of this stabilization are described and discussed. This data, together with hormonal regulation, support the hypothesis that an enzymatic redox system located at the plasma membrane is responsible of the extracellular ascorbate stabilization by HL-60 cells.Abbreviations AFR
ascorbate free radicals
- FCS
fetal calf serum
- Sp-cAMPS
Sp-cyclic adenosine monophosphothionate
- Rp-cAMPS
Rp-cyclic adenosine monophosphothionate 相似文献