Membrane insertion scanning

Membrane Insertion Scanning. Membrane topology of transporter proteins can be... 

The first set of experiments involved fluorescence resonance energy transfer (FRET) between the naphthalene and pyrene-laheled polymers. A 5 1 mixture of PNIPAM-Py to PNIPAM-Na was used. When assembled in micelles, the pyrene acts as a quencher to the naphthalene, leading to high pyrene fluorescence and low naphthalene fluorescence. When the mixture is added to DMPC (liquid phase) or DSPC (gel phase) vesicles at room temperature, naphthalene fluorescence is increased, while pyrene fluorescence is dramatically decreased. This effect is not seen with the PNIPAM-Py-Na polymer, so the reduction in FRET is not due to the hydrophobic environment. This means that the hydrophobic anchors of the PNIPAM-Py and the PNIPAM-Na likely enter the membrane and the dyes are moved apart from one another. The fact that the anchor appeared to insert into the gel-phase DSPC membrane was somewhat surprising. The authors attribute the effect to defects between crystalline domains in the membrane. To test if the LCST transition still occurs when the polymers are anchored to the membrane, differential scanning calorimetry (DFC) was used. The LCST transition of the PNIPAM-Py/PNIPAM-Na mixture in solution was observed in the DFC ttace. When combined with DSPC or DMPC vesicles, the same peak was observed, indicating that the transition does indeed stiU occur, even in the presence of the lipid. 

FIGURE 27.14 (See color insert following page 588.) CVs of a commercial MEA with a 25 pm thick membrane as a function of temperature. Scan rate 50 mV s (ZSW measurements Internal publication). 

On the other hand, the influence of the state of hydration on the photocycle of bacteriorhodopsin is remarkable. In order to study its effect, thin layers of purple membrane were prepared by drying concentrated suspensions of purple membranes in water on a glass sUde at room temperature and atmospheric pressure. Variable hydration of the thin layers was obtained by equilibrating the preparations with various relative humidities produced by saturated salt solutions. The average thickness of the preparation was 1-3 m as determined by scanning electron microscopy. The glass slide containing the preparation was inserted into a cuvette suitable for spectroscopy and equilibrated with the required specific humidity before analysis. 

Water content of the membrane without the electrodes inserted between the cell halves, (a) Without channels, (b) With channels parallel to the scanning direction. (c)With channels perpendicular to the scanning direction. Array 256 x 256, repetition time = 500 ms, echo duration = 18.3 ms, the experiment lasted approximately 1 hour. (Source Bedet et al., 2008b, with permission of Comptes Rendus de I Academie des Sciences.)... 

Ramaswamy (2002) first applied scanning acoustic microscopy for determining the location of pinholes with diameters greater than 100 p,m inserted into commercial micro-porous poly(vinylidene fluoride) (PVDF) membranes as well as for identifying partially penetrating defects with diameters ranging from 100 to 300 p,m. Subsequent work also successfiiUy detected the presence of macrovoid defects in laboratory-cast cellulose-acetate membranes. 

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