Stable cells

The external set-up of different battery systems is generally simple and differs in principle only little from one system to another. A mechanically stable cell case bears the positive and negative electrodes, which are separated by a membrane and are connected with electron-conducting poles. Ion conduction between the electrodes is guaranteed usually by fluid or gel-like electrolyte [13]. 

Bretscher, P.A., Wei, G., Menon,J.N. and Bielefeldt, O.H. (1992) Establishment of stable, cell-mediated immunity that makes susceptible mice resistant to... 

The key function of the vector is to introduce the cDNA under control of a strong promoter and, if a stable cell line is to be developed, also to introduce resistance to a compound that is otherwise toxic to the host cell. This facilitates selection (of only vector-bearing cells grown in special media) of the minority of cells that have... 

The sol-gel-entrapped microbial cells have shown excellent tolerance to different alcohols [99], The immobilized E. coli cells followed the Michaelis-Menten equation when quantified with the (3-glucosidase activity via the hydrolysis of 4-nitrophenyl-(3-D-galactopyranosdie [142], The sol-gel matrices doped with gelatin prevented the cell lysis, which usually occurs during the initial gelation process [143], Microorganisms are now widely used in the biosorption of different pollutants and toxicants. Bacillus sphaericus JG-A12 isolated from uranium mining water has been entrapped in aqueous silica nanosol for the accumulation of copper and uranium [144], Premkumar et al. [145] immobilized recombinant luminous bacteria into TEOS sol-gel to study the effect of sol-gel conditions on the cell response (luminescence). The entrapped and free cells showed almost the same intensity of luminescence (little lower), but the entrapped cells were more stable than the free cells (4 weeks at 4°C). This kind of stable cell could be employed in biosensors in the near future. 

Water is involved in most of the photodecomposition reactions. Hence, nonaqueous electrolytes such as methanol, ethanol, N,N-d i methyl forma mide, acetonitrile, propylene carbonate, ethylene glycol, tetrahydrofuran, nitromethane, benzonitrile, and molten salts such as A1C13-butyl pyridium chloride are chosen. The efficiency of early cells prepared with nonaqueous solvents such as methanol and acetonitrile were low because of the high resistivity of the electrolyte, limited solubility of the redox species, and poor bulk and surface properties of the semiconductor. Recently, reasonably efficient and fairly stable cells have been prepared with nonaqueous electrolytes with a proper design of the electrolyte redox couple and by careful control of the material and surface properties [7], Results with single-crystal semiconductor electrodes can be obtained from table 2 in Ref. 15. Unfortunately, the efficiencies and stabilities achieved cannot justify the use of singlecrystal materials. Table 2 in Ref. 15 summarizes the results of liquid junction solar cells prepared with polycrystalline and thin-film semiconductors [15]. As can be seen the efficiencies are fair. Thin films provide several advantages over bulk materials. Despite these possibilities, the actual efficiencies of solid-state polycrystalline thin-film PV solar cells exceed those obtained with electrochemical PV cells [22,23]. 

To build up a stable cell model according to this concept would mean to isolate membrane proteins and lipids and try to put them together as mother nature does. This idea to use membrane proteins for membrane stabilization does not yet seem to be realizable and therefore simpler possiblities for constructing stable membrane and cell models are desirable. 

In the previous chapters it has been shown that stable cell membrane models can be realized via polymerization of appropriate lipids in planar monolayers at the gas-water interface as well as in spherical vesicles. Moreover, initial experiments demonstrate that polymeric liposomes carrying sugar moieties on their surface can be recognized by lectins, which is a first approach for a successful targeting of stabilized vesicles being one of the preconditions of their use as specific drug carriers in vivo. 

Four possibilities to obtain such a stable cell model that fulfills all the conditions mentioned above are summarized in Figure 15. 

Figure 15. Schematic of the build up of stable cell models via partial polymerization of the membrane. Key

Zahn-Zabal M, Kobr M, Girod PA, Imhof M, Chatellard P, de Jesus M, Wurm F, Mermod N (2001) Development of stable cell lines for production or regulated expression using matrix attachment regions. J Biotechnol 87(l) 29-42... 

Generation of a Stable Cell Line Constitutively Expressing the Tet Repressor... 

R. (2004) A PXR reporter gene assay in a stable cell culture system CYP3A4 and CYP2B6 induction by pesticides. Biochemical Pharmacology, 68,2347-2358. 

Noracharttiyapot, W., Nagai, Y, Matsubara, T., Miyata, M., Shimada, M., Nagata, K. and Yamazoe, Y. (2006) Construction of several human-derived stable cell lines displaying distinct profiles of CYP3A4 induction. Drug Metab. Pharmacokinet., 21, 99-108. 

Initial attempts to purify enzymes from A, parasiticus mycelial extracts that catalyze aflatoxin synthesis were unsuccessful because these enzymes are present in relatively low concentrations and are extremely short-lived (23). Subsequently, several techiuques were examined for disruption of large quantities of mycelia to obtain active and stable cell-fiee preparations (23, 24) pertinent enzymes were recovered from cell-free extracts after grinding mycelia under liquid nitrogen (24). The optimum age of mycelial cultures for recovery of aflatoxin pathway enzymes was determined to be between 72 and 84 h (24a, 25). 

RK is cloned and expressed in SF9 cells [17,23,32] cDNA encoding RK is characterized and sequenced, 561 amino acids protein [22] RK gene expression in baculovirus-infected Sf21 cells [25,30] RK gene is cloned and expressed in Pichia pastoris GS115, COS-1 cells and HEK-293 stable cell line, best in COS-1 cells with correct posttranslational modifications [28] expression of RK and mutants in COS-7 cells [33]) [17, 22, 23, 25, 28, 30, 32, 33] <4> (cDNA encoding enzyme is cloned and expressed in COS-7 cells, sequence of the 561 amino acids protein [13]) [13]... 

Clark, K. R., Voulgaropoulou, F. and Johnson, P. R. (1996). A stable cell line carrying adenovims-inducible rep and cap genes allows for infectivity titration of adeno-associated vims vectors. Gene Ther. 3, 1124—1132. 

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