PubMed · 4899506
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G Cumming. 1969. Disordered respiratory function in emphysema.. https://pubmed.ncbi.nlm.nih.gov/4899506/
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We show that the chemical reactions of the model systems of A+A-->0 and A+B-->0 when performed on scale-free networks exhibit drastically different behavior as compared to the same reactions in normal spaces. The exponents characterizing the density evolution as a function of time are considerably higher than 1, implying that both reactions occur at a much faster rate. This is due to the fact that the discerning effects of the generation of a depletion zone (A+A) and the segregation of the reactants (A+B) do not occur at all as in normal spaces. Instead we observe the formation of clusters of A (A+A reaction) and of mixed A and B (A+B reaction) around the hubs of the network. Only at the limit of very sparse networks is the usual behavior recovered.
Ricin is a promising candidate for the treatment of cancer because it can be selectively targeted to tumor cells via linkage to monoclonal antibodies. Biochemical evidence suggests that escape of ricin or its ribosome-inactivating subunit from an intracellular compartment is mediated by retrograde transport to the endoplasmic reticulum and subsequent direction into the ER-associated degradation pathway. Alternatively, lipase activity of ricin may facilitate leakage from endocytic vesicles. We have observed ricin-mediated release of macromolecular dyes from lipid vesicles that mimic the composition of endosomal membranes. Release of small molecules occurs to the same extent, suggesting an all-or-none mechanism due to bilayer destabilization. The level of accompanying membrane fusion depends on vesicle composition. Since it takes 24 h of incubation before the first traces of lysolipids are detectable by matrix-assisted laser desorption/ionization mass spectrometry, membrane destabilization is not due to the lipase activity of ricin.
We report the design of supported lipid membranes attached to the surface by tailored lipopolymer tethers. A series of well-defined lipopolymers were synthesized by means of living cationic polymerization of 2-methyl-2-oxazolines. The polymers were equipped with a silane coupling group on the proximal, and lipid anchors on the distal chain ends. The length of the intermediate hydrophilic polymer tether was varied (n = 14, 18, 33) to change the distance between the membrane and the substrate. Supported membranes have been prepared in two-steps. First, a suitable lipopolymer/lipid mixture was deposited by Langmuir-Blodgett transfer, and annealed to establish the covalent coupling to the surface. On the dry lipopolymer/lipid monolayer, the upper leaflet was deposited by vesicle fusion. Optimization of both preparation steps resulted in the formation of stable and defect-free membranes. Impacts of the spacer length and the lipopolymer fraction upon the lateral diffusivity of the lipids were systematically compared by fluorescence recovery after photobleaching (FRAP). First experiments on the incorporation of a large transmembrane cell receptor (integrin alpha IIb beta 2) into the polymer-tethered membrane suggested that the length of the polymer tether plays a crucial role in distribution of the proteins on the surface.