PubMed · 660644
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J D Owen. 1978-04-26. Reflection coefficients in red cells.. https://doi.org/10.1007/bf01871149
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The effect of glycosphingolipids (GSLs) with oligosaccharide chains of different length and charge on membrane-membrane interactions induced by myelin basic protein (MBP) or melittin (Mel) was comparatively investigated with small unilamellar vesicles. MBP induces a fast vesicle aggregation and close membrane apposition. Merging of lipid bilayers and vesicle fusion induced by MBP are slower and less extensive processes compared to membrane apposition. The changes of membrane permeability concomitant to these phenomena are small. The Trp region of MBP remains in a rather polar environment when interacting with vesicles; its accessibility to NO3- or acrylamide quenching depends on the type of GSLs in the membrane. The Trp region of Mel is inserted more deeply into the lipid bilayer and its accessibility to the aqueous quenchers is less dependent on variations of the oligosaccharide chain of the GSLs. Mel induces a faster and more extensive membrane apposition and bilayer merging than does MBP. Extensive vesicle disruption occurs in the presence of Mel. Negatively charged GSLs facilitate membrane proximity and vesicle aggregation but an increase of the oligosaccharide chain length of either neutral or acidic GSLs decreases the interaction among vesicles that are induced by either protein. This effect is independent of the different mode of insertion of MBP and Mel into the membrane. Our results suggest that the modulation by the oligosaccharide chain on the protein-induced interactions between bilayers containing GSLs is probably exerted beyond the level of local molecular interactions between the basic proteins and the lipids.
Enterobacter aerogenes mutants with high-level resistance to imipenem were studied. They were derived from strains characterized by stable over-production of a class-I beta-lactamase. This enzyme (pI = 8.2) exhibited high affinity toward imipenem and hydrolysed the drug slowly. Imipenem-resistant mutants lacked a major 43-kDa outer membrane protein and displayed decreased permeability to cephaloridine. Introduction of a plasmid coding for the regulatory ampD gene abolished beta-lactamase production and rendered the mutants susceptible to imipenem.
Factors controlling variability in enzyme transient expression assays have been investigated in electroporated protoplasts isolated from wheat embryogenic and nonembryogenic calli. The level of variation was reduced to a minimum through the optimization of the beta-glucuronidase measurements in the pellet and the supernatant of the homogenized protoplasts, by expressing the data on the basis of the number of protoplasts found to be viable immediately before the assay and on the amount of protein in the pellet and supernatant. Protoplast separation on the basis of size was also useful in eliminating some of the variation resulting from the heterogeneity of the callus used. Efforts to partially synchronize the callus tissue by auxin starvation have not resulted in a significant decrease of this variation. Our results indicate that the level of variation in enzyme transient activity in protoplasts resulting from calli can be reduced by implementation of the experimental techniques presented here.