Media selective agents

Another issue with gene mutation assays is how they allow mutant cells to be identified, visualized, and counted, in order to calculate the mutant frequency. Available methods for endogenous genes consist of using (1) a selective agent to select mutant cells in vitro after cell isolation and transfer to culture medium (e.g.,... 

During this time anew gelatinized 96-well flat-bottom plate with medium (200pL/ well, containing the selection agent) is prepared. 

Transfer leaf discs to shoot regen atirai medium containing 500 mg/litre carbenicillm and appropriate concentration of selective agent for transformed plant cells." Incubate for 21 days at 25 °C with a 16 h photoperiod. 

Selective agent This is a chemical that is added to a medium such that undesirable microorganisms will not grow while desirable microbes will grow. 

Cells are maintained in appropriate culture media (e.g., for CHO cells, Hams F-12 medium is often used, Gibco-BRL, Rockville, MD, cat. no. 11059-029, supplemented with 10% FCS), with appropriate antibiotic and selection agents in the case of engineered ceil lines. Endogenous receptors or transiently transfected cell lines, of course, do not generally need selection. Stocks are described in detail in the case of CHO cells. 

We have found that 6TG is a cleaner selective agent than SAG. Mutation plates with SAG (50 iJLg/m ) as the selective agent are difficult to score, because of the frequent appearance of very small colonies. These small colonies appear even when the mutation plates are periodically refed with fresh SAG medium. No such microcolonies are seen when 6TG (5 Mg/ml) is used as the selective agent. A concentration of 5 fJig/ml 6TG clearly discriminates between mutant and wild-type cells (Figure 2). All 6TG-resistant colonies that we have... 

FiaaHy, ia method (4) the fabric is padded with a mixture of medium energy disperse dyes, carehiUy selected higher reactivity, and rapid diffusiag fiber-reactive dyes, up to 10 g/L sodium bicarbonate depending on depth of shade, and proprietary auxiHary agents. 

Two factors of paramount importance in understanding the chemistry of metal-ammonia reductions are the acidity of the reaction medium and the relative rates of all reactions possible with a given combination of reagents. The control or appreciation of these factors permits one to achieve a certain degree of selectivity in metal-ammonia reductions in spite of the vigor of the reducing agents. 

The initiator in radical polymerization is often regarded simply as a source of radicals. Little attention is paid to the various pathways available for radical generation or to the side reactions that may accompany initiation. The preceding discussion (see 3.2) demonstrated that in selecting initiators (whether thermal, photochemical, redox, etc.) for polymerization, they must be considered in terms of the types of radicals formed, their suitability for use with the particular monomers, solvent, and the other agents present in the polymerization medium, and for the properties they convey to the polymer produced. 

In media selective for enterobacteria a surface-active agent is the main selector, whereas in staphylococcal medium sodium and lithium chlorides are the selectors staphylococci are tolerant of salt concentrations to around 7.5%. Mannitol salt, Baird-Parker (BP) and Vogel-Johnson (VJ) media are three examples of selective staphyloccocal media. Beside salt concentration the other principles are the use of a selective carbon source, mannitol or sodium pyruvate together with a buffer plus acid-base indicator for visualizing metabolic activity and, by inference, growth. BP medium also contains egg yolk the lecithin (phospholipid) in this is hydrolysed by staphylococcal (esterase) activity so that organisms are surrounded by a cleared zone in the otherwise opaque medium. The United States Pharmacopeia (1990) includes a test for staphylococci in pharmaceutical products, whereas the British Pharmacopoeia (1993) does not. 

Finally, Jessop and coworkers describe an organometalhc approach to prepare in situ rhodium nanoparticles [78]. The stabilizing agent is the surfactant tetrabutylammonium hydrogen sulfate. The hydrogenation of anisole, phenol, p-xylene and ethylbenzoate is performed under biphasic aqueous/supercritical ethane medium at 36 °C and 10 bar H2. The catalytic system is poorly characterized. The authors report the influence of the solubility of the substrates on the catalytic activity, p-xylene was selectively converted to czs-l,4-dimethylcyclohexane (53% versus 26% trans) and 100 TTO are obtained in 62 h for the complete hydrogenation of phenol, which is very soluble in water. 

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