Membrane aggregation

Figure 39. Circular dichroism spectra of heavy beef heart mitochondria in KCI as a function of sonication, which causes the membrane aggregates to decrease in size. As the size of the aggregate decreases, there is a progressive increase in the magnitude of the elliptiiaty and a shifting of the location of the negative extremum to 222 nm. These changes are due to particle size-dependent distortions in the CD spectra. Most pronounced is the effect on the magnitude of the bands, including the 222 nm band. Reproduced, with permission, from [105].

Many applications rely on enzymes being retained by membranes, aggregated by cross-linking, or immobilized by encapsulation. These techniques are often simple and inexpensive, but typically also generate a poorly defined immobilized enzyme. The immobilization can involve isolated enzymes or whole cell preparations. Sweetzyme IT, an immobilized glucose isomerase produced by Novozymes is an example of the latter, in which the cells are cross-linked by glutaraldehyde (GA) and extruded to produce dry, solid particles [32]. 

Membrane Aggregation. Isolated thylakoids form stable suspensions at neutral pH, since the membranes carry a net negative charge. During thawing of thylakoid suspensions which have been frozen in salt solutions the membranes aggregate and precipitate. This indicates a reduction in the net charge of the membranes. Precipitation does not... 

To overcome the problem of aggregation, planar artificial membranes have been used such as phospholipid monolayers at the air-water interface [33-35] and SSMs [36-39]. By means of SSMs, the primary binding of annexin can be readily separated from membrane aggregation, which involves two membrane interfaces. 

One of the functions of annexin A1 is to connect the plasma membrane with another membrane located in the cell as a function of the calcium ion concentration in the cytosol [28,32,36]. In order to prove that annexin A1 is capable of interconnecting two membranes, aggregation assays on 5-MHz quartz resonators were performed as schematically depicted in Fig. 11. 

While vibrational spectroscopy is not capable of the structural resolution of X-ray diffraction, it nevertheless has some important advantageous features. First, it is not generally limited by physical state samples can be in the form of powders, crystals, films, solutions, membranous aggregates, etc. Second, a number of different experimental methods probe the structure-dependent vibrational modes of the system infrared (IR), Raman (both visible and UV-exeited resonance), vibrational circular dichroism, and Raman optical activity, many of these with time-resolution capabilities. Finally, in addition to providing structural information, vibrational spectra are sensitive to intra- and intennolecular interaction forces, and thus they also give information about these properties of the system. 

PYROGALLOL[4]ARENE MEMBRANE AGGREGATION—PLANAR BILAYER STUDIES... 

Verity et al. (1968) obtained biphasic curves when the release of acid phosphatase from lysosomal fraction was studied as a function of Ca and Mg concentrations. Results of sucrose density gradient centrifugation of the frozen-and-thawed disrupted lysosomal fraction in different ions suggested membrane aggregation and enzyme-membrane association in the presence of divalent cations, (See Chapter by Verity). 

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