Erythrocyte membrane vesiculation: model for the molecular mechanism of protein sorting

Budding and vesiculation of erythrocyte membranes occurs by a process involving an uncoupling of the membrane skeleton from the lipid bilayer. Vesicle formation provides an important means whereby protein sorting and trafficking can occur. To understand the mechanism of sorting at the molecular level, we have developed a micropipette technique to quantify the redistribution of fluorescently labeled erythrocyte membrane components during mechanically induced membrane deformation and vesiculation. Our previous studies indicated that the spectrin-based membrane skeleton deforms elastically, producing a constant density gradient during deformation. Our current studies showed that during vesiculation the skeleton did not fragment but rather retracted to the cell body, resulting in a vesicle completely depleted of skeleton. These local changes in skeletal density regulated the sorting of nonskeletal membrane components. Highly mobile membrane components, phosphatidylethanolamine- and glycosylphosphatidylinositol-linked CD59 with no specific skeletal association were enriched in the vesicle. In contrast, two components with known specific skeletal association, band 3 and glycophorin A, were differentially depleted in vesicles. Increasing the skeletal association of glycophorin A by liganding its extrafacial domain reduced the fraction partitioning to the vesicle. We conclude that this technique of bilayer/skeleton uncoupling provides a means with which to study protein sorting driven by changes in local skeletal density. Moreover, it is the interaction of particular membrane components with the spectrin-based skeleton that determines molecular partitioning during protein sorting.     

SHEAR AND INTERFACIAL INSTABILITIES OF OIL-WATER FLOW IN AN INCLINED CHANNEL

A study of the linear stability of a laminar flow of an oil-water system in an inclined channel is presented. A novel shear-mode of instability, which is necessarily decaying in plane Poiseuille flow, is found to be the primary instability in certain situations. When the channel is sufficiently inclined, the long-wave mode can become unstable, regardless of the total volumetric flow rate of the fluids The consequences to oil transport are discussed.     

Sized controlled synthesis, purification, and cell studies with silicon quantum dots

This article describes the size control synthesis of silicon quantum dots with simple microemulsion techniques. The silicon nanocrystals are small enough to be in the strong confinement regime and photoluminesce in the blue region of the visible spectrum and the emission can be tuned by changing the nanocrystal size. The silicon quantum dots were capped with allylamine either a platinum catalyst or UV-radiation. An extensive purification protocol is reported and assessed using (1)H NMR to produce ultra pure silicon quantum dots suitable for biological studies. The highly pure quantum dots were used in cellular uptake experiments and monitored using confocal microscopy. The results showed that the amine terminated silicon nanocrystals accumulated in lysosome but not in nuclei and could be used as bio-markers to monitor cancer cells over long timescales.     

The Influence of Surface Modification on the Epoxidation Selectivity and Mechanism of TiSBA15 and TaSBA15 Catalysts with Aqueous Hydrogen Peroxide

The thermolytic molecular precursor method was used to introduce site-isolated Ti(IV) and Ta(V) centers onto the surface of a mesoporous SBA15 support. The resulting surface SiOH, TiOH, and TaOH sites were modified with a series of (N,N-dimethylamino)trialkylsilanes, Me₂NSiMe₂R (where R = Me, ⁿ Bu, or ⁿ Oc). Compared to the unmodified catalysts, the surface-modified catalysts are more active in the epoxidation of cyclohexene with H₂O₂ and exhibit a markedly greater selectivity for cyclohexene oxide (up to 58% for Ti(IV) and greater than 95% for Ta(V)). In situ spectroscopies were used to probe this phenomenon, and it was determined that a siloxy-capped Ti(IV) or Ta(V) site is essential to achieve the high epoxide selectivity.