Lymphokines which influence electrophoretic mobility of macrophages.

Supernatants of blood lymphocytes from immunized guinea pigs after incubation with purified protein derivative (PPD) were fractionated on Sephadex G-75. The fractions were tested for activity to change the electrophoretic mobility of macrophages. Dependent on incubation time, three different regions of activity with an average molecular weight of 13 000, 40 000 and more than 100 000 were estimated.     

The influence of unipolar air ions on the electrophoretic mobility of erythrocytes

Positive air ions decreased the electrophoretic mobility of erythrocytes of cats while negative air ions increased it. Inhalation of normal air supplied by a fan did not affect the electrophoretic mobility of erythrocytes.

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Zusammenfassung Positive Luftionen setzten die elektrophoretische Beweglichkeit der Erythrocyten von Katzen herab, während negative Luftionen sie steigerten. Die Inhalation normaler Luft, die von einem Ventilator unterstüzt wurde,beeinflusste die elektrophoretische Beweglichkeit von Erythrocyten nicht.

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Resume Les ions positifs diminuent la mobilité électrophorétique des érythrocytes des chats, alors que les ions négatifs l'augmentent. L'inhalation d'air normal,même activée par un ventilateur, ne l'influence par contre pas.

     

DNA chain length markers and the influence of base composition on electrophoretic mobility of oligodeoxyribonucleotides in polyacrylamide-gels.

The specific influence of the four nucleobases on electrophoretic mobility of oligodeoxyribonucleotides in polyacrylamide-gels under denaturing and nondenaturing conditions has been investigated using homooligomers from the four deoxyribonucleotides as chain length standards. Homooligomers of same chain lengths exhibit remarkable differences in mobility. Specific retardation of any other oligonucleotide investigated was found to be mainly dependent on base composition but not on sequence. A simple procedure is presented for calculating mobilities relative to the standards on denaturing gels. This allows a reliable identification of oligonucleotides on acrylamide-gels by exact chain length determination with respect to base composition and furthermore a detailed interpretation of complex reaction mixtures. The homooligomers also show the same differences in mobility on nondenaturing gels. The significance of this effect for strand separation is discussed.     

Temperature dependence of the gel electrophoretic mobility of superhelical DNA.

We have determined the gel electrophoretic behavior of closed circular plasmid pSM1 DNA (5420 bp) as a function of both temperature and of linking number (Lk). At temperatures below 37 degrees, the electrophoretic mobility first increases, then becomes constant as Lk is decreased below that of the relaxed closed DNA. As the temperature is increased above 37 degrees the electrophoretic mobility first increases as Lk decreases and then varies in a cyclic manner with further decreases in Lk. As the temperature is increased over the range 37 degrees - 65 degrees the cyclic behavior is manifested at progressively smaller decreases in Lk and the amplitude of the cycles increases. We interpret the results in terms of the early melting of superhelical DNA, in which the free energy associated with superhelix formation is progressively transferred to local denaturation. Using a two state approximation, we estimate the free energy change in the first cyclic transition to be 35 Kcal/mole DNA at 37 degrees and to decrease linearly with temperature. The free energy becomes equal to zero at a temperature of 71.6 degrees, which lies within 3 degrees of the melting temperature for the corresponding nicked circular DNA. From the slope of this relationship we estimate the apparent entropy and enthalpy of the first mobility transition to be 6.0 Kcal/mole base pair and 17.3 cal/mole base pair/degree, values consistent with duplex melting.     

Antibiotic induced electrophoretic mobility shifts of DNA restriction fragments.

Several antibiotics, netropsin, distamycin A, actinomycin D, Hoechst 33258 and olivomycin, which demonstrate base specificity in their DNA binding properties have been found to alter the electrophoretic mobility of DNA restriction fragments in native polyacrylamide gels. The antibiotics mostly reduced the migration of larger DNA fragments, but netropsin and Hoechst 33258 were observed to increase the migration rate of several DNA fragments of intermediate size. DNA fragments of similar molecular weight which comigrate as a single gel band can at times be separated as the result of differential mobility shifts promoted by antibiotic DNA complex formations.     

Effects of DNA charge and length on the electrophoretic mobility of intercalated DNA

DNA molecules ranging in size from 1 to 630 kilobase pair and intercalated with either ethidium bromide (EtBr) or propidium iodide (PI) were electrophoresed in 1% agarose at four different electric field strengths. The extent of intercalation of EtBr under the conditions of our electrophoresis experiments was determined by a spectroscopic technique, whereas the extent of intercalation of PI was inferred from previous studies. The effects of the increase in DNA contour length and the concomitant decrease of linear charge density were separated based on our analysis of the mobility data. We conclude that the main factor responsible for the reduced electrophoretic mobility of intercalated DNA is the diminished linear charge density and not the increased contour length. © 1994 John Wiley & Sons, Inc.     

The interactions between the fluorescent dye thiazole orange and DNA

The interaction of the fluorescent dye thiazole orange (TO) with nucleic acids is characterized. It is found that TO binds with highest affinity to double-stranded (ds) DNA [log(K) ≈ 5.5 at 100 mM salt], about 5–10 times weaker to single-stranded polypurines, and further 10–1000 times weaker to single-stranded polypyrimidines. TO binds as a monomer to dsDNAs and poly(dA), both as a monomer and as a dimer to poly(dG) and mainly as a dimer to poly(dC) and poly(dT). The fluorescence quantum yield of TO free in solution is about 2 · 10⁻⁴, and it increases to about 0.1 when bound to dsDNA or to poly(dA), and to about 0.4 when bound to poly(dG). Estimated quantum yields of TO bound to poly(dC) and poly(dT) are about 0.06 and 0.01, respectively. The quantum yield of bound TO depends on temperature and decreases about threefold between 5 and 50°C. © 1998 John Wiley & Sons, Inc. Biopoly 46: 39–51, 1998     

Dependence of the electrophoretic mobility of DNA in gels on field intermittency

The electrophoretic mobility of double helical DNA in agarose and polyacrylamide gels increases as a function of time after the electric field is applied to the gel and decreases after the field is terminated. The changes are large for long (more than 10 kb) molecules. The effects of other variables are indicated.     

Modeling the free solution electrophoretic mobility of short DNA fragments

Boundary element methods are used to model the free solution electrophoretic mobility of short DNA fragments. The Stern surfaces of the DNA fragments are modeled as plated cylinders that reproduce translational and rotational diffusion constants. The solvent-accessible and ion-accessible surfaces are taken to be coincident with the Stern surface. The mobilities are computed by solving simultaneously the coupled Navier–Stokes, Poisson, and ion-transport equations. The equilibrium electrostatics are treated at the level of the full Poisson–Boltzmann equation and ion relaxation is included. For polyions as highly charged as short DNA fragments, ion relaxation is substantial. At .11 M KCl, the simulated mobilities of a 20 base pair DNA fragment are in excellent agreement with experiment. At .04 M Tris acetate, pH = 8.0, the simulated mobilities are about 10–15% higher than experimental values and this discrepancy is attributed to the relatively large size of the Tris counterion. The length dependence of the mobility at .11 M KCl is also investigated. Earlier mobility studies on lysozyme are reexamined in view of the present findings. In addition to electrophoretic mobilities, the effective polyion charge measured in steady state electrophoresis and its relationship to the preferential interaction parameter γgG is briefly considered. © 1998 John Wiley & Sons, Inc. Biopoly 46: 359–373, 1998     

Presence of single-stranded DNA in PCR products of slow electrophoretic mobility.

PCR products were characterized by electrophoresis, blotting and hybridization. In addition to the bands of expected size, bands of slower electrophoretic mobility were often detected. The slower bands completely disappeared when the PCR products were subjected to slow cooling, treated with S1 nuclease or run on an alkaline gel, whereas the bands of expected size were unaffected. The slower bands are therefore likely to contain single-stranded DNA.     

Gel electrophoretic mobility evaluation of a necklace-like DNA nanostructure

DNA nanotechnologies have been highlighted as a promising synthetic tool for the creation of new shaped materials. They have developed a variety of materials in different shapes and sizes [1]. Inspired by these advancements, we sought to design a ring-shaped DNA nanostructure connected by X-DNA blocks. Six XDNA blocks were ligated together to form a circular nanostructure with a diameter of approximately 30 nm. Each DNA block possesses different overhang sequences in its terminal. It was sequentially built up onto each block platform in the line and later clipped into a necklace shape via enzymatic ligation. It was finally evaluated by a gel electrophoretic migration shift assay. It was concluded that the complete set of the necklace shaped DNA nanostructure was the most slowly retarded relative to other forms of incompleteness.     

Computation of the electrophoretic mobility of proteins.

A scheme is presented for computing the electrophoretic mobility of proteins in free solution, accounting for the details of the protein shape and charge distribution. The method of Teubner is implemented using a boundary integral formulation within which the velocity distribution, the equilibrium electrical potential around the molecule, and the potential distribution due to the applied field are solved for numerically using the boundary element method. Good agreement of the numerical result is obtained for spheres with the corresponding semi-analytical specialization of Henry's analysis. For protein systems, the method is applied to lysozyme and ribonuclease A. In both cases, the predicted mobility tensors are fairly isotropic, with the resulting scalar mobilities being significantly smaller than for spheres of equal volume and net charge. Comparisons with previously published experimental results for ribonuclease show agreement to be excellent in the presence of a net charge, but poorer at the point of zero charge. The approach may be useful for evaluating approximate methods for estimating protein electrophoretic mobilities and for using electrophoretic measurements to obtain insight into charge distributions on proteins.     

Topological effects on the electrophoretic mobility of rigid rodlike DNA in polyacrylamide gels

The electrophoretic migration of rigid rodlike DNA structures with well defined topologies has been investigated in polyacrylamide (PA) hydrogels prepared by copolymerization of acrylamide and N, N'-methylenebisacrylamide. Previous studies have reported structural and dynamic characteristics of linear and branched DNA during electrophoresis in PA gels using a variety of experimental parameters. However, a thorough investigation aimed at establishing specific relationships between topological features of rigid rodlike DNA structures and their electrophoretic behavior is still needed. In order to study these topological effects on mobility, an intensive examination of the electrophoretic mobility of small linear and starlike DNA was performed. A series of model DNA structures with well-defined branched topologies were synthesized with varying molecular parameters, such as number of arms surrounding the branch point and arm length. The electrophoretic mobility of these structures was then contrasted with a series of data obtained using linear DNA of comparable molecular size. When large DNA stars (M >/= 60 bp) were compared with linear DNA of identical molecular weight, the Ferguson plots were quite different. However, small DNA stars (24-32 bp) and linear analogues had identical Ferguson plots. This indicates that a different motional mode or greater interaction with the gel exists for the larger DNA stars. When the total molecular weight of the DNA stars was held constant and the number of arms varied, the Ferguson plots for all the stars were identical. Additionally, a critical pore size was reached when the ratio of linear DNA mobility to star DNA mobility increased dramatically. Thus, while the incorporation of a single branch point can produce a large reduction in mobility, above a critical molecular size, the incorporation of additional branch points does not appear to provide further reduction in mobility. This finding is consistent with the transport properties of large synthetic star polymers, where a large reduction in their diffusion coefficient is observed when a single branch is added. When additional arms are incorporated, large synthetic stars do not display an appreciable further reduction in diffusion coefficient. The effect of arm length on mobility for rigid rod DNA stars was also studied. For four-arm DNA stars, the mobility was found to scale as an exponential function of the arm length. Finally, a recently proposed phenomenological model was used to successfully fit the mobility data for linear rigid rod DNA at various concentrations of PA.     

Tracts of A.T base pairs retard the electrophoretic mobility of short DNA duplexes.

An investigation of the mobility of short duplexes of DNA -octamers and decamers-on polyacrylamide gels is presented, showing that molecules containing less than one helical turn exhibit sequence dependent mobilities. Analysis of chains with different sequences indicates that any arrangement of two or more adjacent A.T base pairs causes a duplex to move more slowly than does any combination of isolated A.T pairs This behavior appears to be an intrinsic property of these sequences, since the anomaly persists in the absence of magnesium or presence of spermine and is not due to strand dissociation. In two decamers we studied, the position of A.T tracts within a duplex can be shown to influence mobility: the sequence GA4T4C associated with bending or curvature of the helix axis when ligated into polymers migrates more slowly than the corresponding sequence GT4A4C, polymers of which migrate as linear B DNA.