Protein-polymeric membrane

Protein-polymeric membrane in a microchannel is prepared by using a concentric laminar flow (Fig. 43) [267]. Crosslinking condensation of a crosslinked enzyme aggregate (CLEA) [268] with aldehyde groups, which react with amino groups of the enzyme, in a concentric laminar flow results in the formation of a cylindrical enzyme-polymerized membrane on the inner wall of the microtube. The use of this technology for membrane formation in a microchannel can be extended to a broad range of functional proteins. 

Because membrane filtration is the only currently acceptable method of sterilizing protein pharmaceuticals, the adsorption and inactivation of proteins on membranes is of particular concern during formulation development. Pitt [56] examined nonspecific protein binding of polymeric microporous membranes typically used in sterilization by membrane filtration. Nitrocellulose and nylon membranes had extremely high protein adsorption, followed by polysulfone, cellulose diacetate, and hydrophilic polyvinylidene fluoride membranes. In a subsequent study by Truskey et al. [46], protein conformational changes after filtration were observed by CD spectroscopy, particularly with nylon and polysulfone membrane filters. The conformational changes were related to the tendency of the membrane to adsorb the protein, although the precise mechanism was unclear. 

What reasons are there for mixing polymerizable lipids with natural ones Polymerized membrane systems, especially those based on diacetylenic lipids, have proven to be excessively rigid and to show no phase transition. Addition of natural lipids could help to retain a certain membrane mobility even in the polymerized state, with almost unaffected stability. Furthermore, natural lipids can provide a suitable environment for the incorporation of membrane proteins into polymerizable membranes (see 4.2.3). Besides this, enzymatic hydrolysis of the natural membrane component can be used for selectively opening up a vesicle in order to release entrapped substances in a defined manner (see 4.2.2). Therefore, it is interesting to learn about the miscibility of polymerizable and natural lipids and also about the polymerization behavior of these mixtures. Investigations on this subject have thus far focused on mixtures of natural lipids with polymerizable lipids carrying diacetylene moieties. 

Incorporation of Membrane Proteins into Polymeric Membranes... 

A straightforward way to collect solutes from the interstitial fluid (ISF) space would be to have a semipermeable, hollow fiber, membrane-based device as originally described by Bito et al.1 Two semipermeable membrane-based devices that have been used to collect different types of analytes from various mammalian tissues include microdialysis sampling probes (catheters) and ultrafiltration probes. The heart of each of these devices is the semipermeable polymeric membrane shown in Figure 6.1. The membranes allow for collection of analytes from the ISF that are below the membrane molecular weight cutoff (MWCO). Each of these devices provides a sample that has a significantly reduced amount of protein when compared to either blood or tissue... 

In an earlier investigation by the author [1] electrophoresis protein separation membranes were prepared using triacryloyl-tris(2-aminoethyl)amine, (I), tri-methacryloyl-tris(2-aminoethyl)amine, (II), and polyethylenimine acrylates, (III). These agents were polymerized either by using ammonium persulphate or photolytically. 

The ultrafiltration process is operated in a batch mode at a temperature of about 50 C. Ceramic membranes with 0.1 or 0.2 pm pore diameter enable processing of this highly viscous and concentrated raw or pasteurized whole milk due to their inherent mechanical strength. The viscosity of the concentrate has been found to increase exponentially with the rise of protein content in the precheese. Polymeric membranes have also been considered not suitable for this process in view of their structural compaction under pressure and their difficulty of cleaning. 

Separation of plasma from blood can be used to remove toxic substances with high molecular weights in body fluid which is important in the treatment of many fatal diseases [Nose et al., 1983] and to collect plasma for blood banks to produce plasma fractionates [Dceda et al., 1986]. Organic polymeric membranes with a mean pore diameter finer than 0.5 pm have been employed to some extent for these purposes. However, their wide pore size distributions and protein adhesion problems make their permeate flux quickly decline and their separation efficiency low. In addition, polymeric membranes generally can not withstand sterilization by autoclaves or chemical cleaning. 

Most chemical cleaning protocols consist of an alkali detergent step followed by an acid step, with appropriate rinses in between. However, for polymeric membranes, it is also common to follow the acid cleaning step with a second alkali cleaning step supplemented with chlorine as this further improves flux [176,179]. In some cases, acid cleaning has been recommended as the first step, especially for whey applications, where mineral fouling maybe more important than protein fouhng [176]. 

Figure l-P depicts only early events in the history of a secreted protein or membrane-bound protein, namely, the polymerization of amino acids and inser-... 

W.J. Dillman and l.F. Miller, On the adsorption of serum proteins on polymeric membrane surfaces. /. Colloid Interface Sci., 44 (1973) 221. 

Microfiltration of whey prior to ultrafiltration in the production of whey protein concentrates (WPC) was reported among others by Maubois et al. [75], van der Horst [76], and Wnuk et al. [77]. The microfiltration step cdso prevents fouling of the UF-membranes (either polymeric membranes or ceramic membrane) e.g. Daufin et al. [78] by phosphates and calcium. 

The separation of proteins and enzymes is performed with ultrafiltration membranes. Branger et al. [93] use Carbosep Ml and M4 (40,000 and 20,000 Dalton respectively) for the separation of enzyme hydrolysates. The fluxes with these membranes compare favourably with polymeric membranes 37-102 l/m hvs. 7-41 l/m h. 

The lateral segregation mechanism of FPR desensitization in neutrophils (Figure 2) may be an attractive model that integrates the receptor-mediated actin polymerization/depolymerization and feed-back regulation of receptor fimction. What do we know about FPR binding to cytoskeletal proteins and membrane disribution of FPR as a function of the activation state of neutrophils to support such an idea ... 

In the area of aflatoxin problems, cultures of Pseudomonas sp. have been observed to have efficacy to destroy the toxin in concentration up to 200 ppb similarly, culture filtrates of a strain of P. aeruginosa exhibited the ability to completely eliminate aflatoxin (10 pmg to nil ) through excretion of a low molecular weight protein acetylcholineesterase immobilized on polymeric membranes by gelatin entrapment [65]. 

Siwy et al. demonstrated the utility of a single conically shaped gold nanotube that was embedded in a mechanically and chemically robust polymeric membrane [142]. They reported biofunctionalized conical Au nanotubes, which are potentially useful for obtaining highly sensitive and selective protein biosensors. So et al. introduced a single walled carbon nanotube field effect transistor (SWNT-FET) combined with aptamers as an alternative to the corresponding antibody [143]. 

Microporous polymeric membranes are used widely for filtration and purification processes, such as filtration of wastewater, preparation of ultra-pure water, and in medical, pharmaceutical or food applications, including removal of microorganisms, dialysis and protein filtration. 

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