Electrophoresis mobilities

The time quoted for the first dimension electrophoresis is suitable for proteins that migrate relatively fast, like aj-antichymotrypsin. For glycoproteins with a low electrophoresis mobility, this time should be lengthened and the appropriate time for the first dimension run should be determined in initial trial experiments. 

Experiment to demonstrate that ax-[Pt(NH3)2 d(pGpG) ] intrastrand crosslinks bend duplex DNA by =34°. Panel A shows the platinated 22-mer sequence, panel B the effect of platination on the gel-electrophoresis mobility of the 22-mer (P22) and a control 27-mer (P27) oligomers, and panel C the mobility of copolymerized DNAs containing cis-DDP and A-tract induced bends ( , 128-bp Pt -t- A-tract DNA 0,96-bp Pt -P A-tract DNA) that maximize at approximately halfintegral helical turns corresponding to their phasing. For more detail consult Reference 93. 

One-dimensional pulsed electrophoresis (ODP) can size fractionate large DNA molecules. One experimental arrangement applies a relatively short electrical pulse followed by a much longer period of zero field strength (2,12). Presumably, during the field-on condition, molecular conformation is perturbed and relaxation then takes place during the field-off condition. As with TDP electrophoresis, mobility can be modulated with different pulse times. 

Capillary Electrophoresis Mobile phase Cyclodextrin Derivatives Chiral Surfactants (MEKC) Poly(saccharides) Glycopeptides Proteins Metal Chelates... 

The previous section illustrated the diversity of DNA sequence-directed structure and dynamics as assessed by many techniques, including NMR, crystallography, hydrodynamic and electrooptical methods, gel electrophoresis mobility and circularization studies, and scanning probe microscopies. Why then is it of interest to develop photophysical probes of such structures and dynamics, given the wealth of data that already exist The following arguments can be made (aside from pure scientific interest) ... 

Slater, GW. and Noolandi, J., The biased reptation model of DNA gel electrophoresis mobility vs. molecular size and gel concentration, Biopolymers, 28, 1781, 1989. 

Electrophoresis refers to the motion of a charged particle in a solution in response to an applied electric field. The electrophoresis technique has been widely used to characterize the electrokinetic properties of charged particle-liquid interfaces. In the electrophoresis method, fine particles (usually of 1 pm in diameter) are dispersed in a solution. Under an applied electric field, the particle electrophoresis mobility, vg, defined as the ratio of particle velocity to electric field strength, is measured using an appropriate microscopic technique. The particle -potential is determined from the measured electrophoresis mobility, ve, by using the Smoluchowski equation expressed as... 

Fried MG (1989) Measurement of protein-DNA interaction parameters by electrophoresis mobility shift assay. Electrophoresis 10(5-6) 366-376. doi 10.1002/elps.ll50100515... 

The soluble derivatives were subjected to binding studies on plasmid DNA monitored by agarose gel Electrophoresis Mobility Shift Assays (EMSA). Here... 

Certain enzymes exist in several different forms termed isoenzymes which are distinguishable by electrophoresis (mobility in an electric current) and by their immimochemistry. The different forms of the enzyme may occur in different tissues or alter in their relative proportions within the same tissue with time. The case which has been most studied is that of the five isoenzymes of lactate dehydrogenase which occur in mammalian tissues. Each isoenzyme has the same molecular weight (135,000) and is built up of foiu- polypeptide chains of two kinds (a and j8). The isoenzymes differ in their a, p make up thus 4a, 4j8, la + 3/S, 2a + 2/S, 3a - - 1/3. At least 33 different enzymes have been reported to exist as isoenzymes in plant tissues. 

The effect known either as electroosmosis or electroendosmosis is a complement to that of electrophoresis. In the latter case, when a field F is applied, the surface or particle is mobile and moves relative to the solvent, which is fixed (in laboratory coordinates). If, however, the surface is fixed, it is the mobile diffuse layer that moves under an applied field, carrying solution with it. If one has a tube of radius r whose walls possess a certain potential and charge density, then Eqs. V-35 and V-36 again apply, with v now being the velocity of the diffuse layer. For water at 25°C, a field of about 1500 V/cm is needed to produce a velocity of 1 cm/sec if f is 100 mV (see Problem V-14). 

Electrophoresis is used primarily to analyze mix tures of peptides and proteins rather than individual ammo acids but analogous principles apply Because they incorporate different numbers of ammo acids and because their side chains are different two pep tides will have slightly different acid-base properties and slightly different net charges at a particular pH Thus their mobilities m an electric field will be differ ent and electrophoresis can be used to separate them The medium used to separate peptides and proteins is typically a polyacrylamide gel leading to the term gel electrophoresis for this technique... 

First, solutes with larger electrophoretic mobilities (in the same direction as the electroosmotic flow) have greater efficiencies thus, smaller, more highly charged solutes are not only the first solutes to elute, but do so with greater efficiency. Second, efficiency in capillary electrophoresis is independent of the capillary s length. Typical theoretical plate counts are approximately 100,000-200,000 for capillary electrophoresis. 

A form of capillary electrophoresis in which separations are based on differences in the solutes electrophoretic mobilities. 

Electroultrafiltration (EUF) combines forced-flow electrophoresis (see Electroseparations,electrophoresis) with ultrafiltration to control or eliminate the gel-polarization layer (45—47). Suspended colloidal particles have electrophoretic mobilities measured by a zeta potential (see Colloids Elotation). Most naturally occurring suspensoids (eg, clay, PVC latex, and biological systems), emulsions, and protein solutes are negatively charged. Placing an electric field across an ultrafiltration membrane faciUtates transport of retained species away from the membrane surface. Thus, the retention of partially rejected solutes can be dramatically improved (see Electrodialysis). 

The use of standards with samples makes zone electrophoresis particulady usehil as an analytical tool. However, when samples caimot be analyzed on the same gel, differences in the experimental conditions from experiment to experiment make direct comparison more difficult. To make comparisons from experiment to experiment, a relative mobility, is often measured by measuring the distance a component travels down the gel compared to some reference or standard component. 

Electroosmotic flow in a capillary also makes it possible to analyze both cations and anions in the same sample. The only requirement is that the electroosmotic flow downstream is of a greater magnitude than electrophoresis of the oppositely charged ions upstream. Electro osmosis is the preferred method of generating flow in the capillary, because the variation in the flow profile occurs within a fraction of Kr from the wall (49). When electro osmosis is used for sample injection, differing amounts of analyte can be found between the sample in the capillary and the uninjected sample, because of different electrophoretic mobilities of analytes (50). Two other methods of generating flow are with gravity or with a pump. 

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