Isoelectric Focusing and Isotachophoresis of Proteins

Isotachophoresis: Theory and Microfluidic Applications

Isotachophoresis (ITP) is a versatile electrophoretic technique that can be used for sample preconcentration, separation, purification, and mixing, and to control and accelerate chemical reactions. Although the basic technique is nearly a century old and widely used, there is a persistent need for an easily approachable, succinct, and rigorous review of ITP theory and analysis. This is important because the interest and adoption of the technique has grown over the last two decades, especially with its implementation in microfluidics and integration with on-chip chemical and biochemical assays. We here provide a review of ITP theory starting from physicochemical first-principles, including conservation of species, conservation of current, approximation of charge neutrality, pH equilibrium of weak electrolytes, and so-called regulating functions that govern transport dynamics, with a strong emphasis on steady and unsteady transport. We combine these generally applicable (to all types of ITP) theoretical discussions with applications of ITP in the field of microfluidic systems, particularly on-chip biochemical analyses. Our discussion includes principles that govern the ITP focusing of weak and strong electrolytes; ITP dynamics in peak and plateau modes; a review of simulation tools, experimental tools, and detection methods; applications of ITP for on-chip separations and trace analyte manipulation; and design considerations and challenges for microfluidic ITP systems. We conclude with remarks on possible future research directions. The intent of this review is to help make ITP analysis and design principles more accessible to the scientific and engineering communities and to provide a rigorous basis for the increased adoption of ITP in microfluidics.

Detection of biochemical mutants in mice

Several bioanalytical techniques including electrofocusing, two-dimensional technique comprising electrofocusing and electrophoresis, and chromatography have been evaluated and improved to provide a method for detecting gene mutations in mice. The use of 1 mm gels for both electrofocusing and electrophoresis in the two-dimensional technique resulted in better resolution, shorter separation time, and reduced costs. An electrophoretic apparatus for the second direction electrophoresis has been designed which eliminated cutting of a flat gel into strips prior to electrophoresis. These changes reduced the total time for a two-dimensional separation to 4 h. The scope and application of isoelectric focusing in detecting gene mutations in mice have been improved by the agar contact replica method. This method allows the simultaneous analysis of several genetic loci besides facilitating automation of evaluation, documentation, and storage of zymograms. Preliminary studies on the detection of heritable metabolic disorders of amino acid metabolism in mice show a potential for such studies in estimating mutation rates in mice. Some possible techniques for such studies and their implications are discussed.

Effects of diethylstilbestrol on the production of various extracellular products of Staphylococcus aureus

The synthetic estrogen diethylstilbestrol at a subinhibitory level of 1.75 microng/ml diminished the production of staphylococcal alpha toxin, coagulase, deoxyribonuclease and penicillinase. Thus, the reported host beneficial effects of diethylstilbestrol may be partially related to its retardive action of certain toxins, or enzymes of S. aureus.

Studies of an acidic cardiotoxin isolated from the venom of Mojave rattlesnake (Crotalus scutulatus)

A major lethal protein was isolated from the venom of Mojave rattlesnake (Crotalus scutulatus) by successive purification in DEAE column chromatography and isoelectric focusing. This homogeneous and monomeric form of toxin is designated as "Mojave toxin". Unlike basic neurotoxins or cytotoxins isolated from venoms of cobras, kraits and sea snakes, the Mojave toxin is an acidic protein with an isoelectric point of 4.7. The toxin is also different from crotoxin (from Crotalus durissus terrificus) which consists of both acidic and basic components. The molecular weight determined by Sephadex G-75 column chromatography resulted in a value of about 22 000. A singel protein band with a molecular weight of about 12 000, was observed after sodium dodecyl sulfate gel electrophoresis of the reduced Mojave toxin. Isoelectric focusing gel in the presence of 8 M urea also showed a single protein band, suggesting that the toxin is composed of subunits. Unlike the neurotoxic nature of the basic proteins from the venoms of Elapidae and sea snakes (Hydrophiidae) and crotoxin, Mojave toxin is cardiotoxic rather than neurotoxic. It is very likely that venoms of all rattlesnakes from North and Central America contain Mojave toxin as the common toxin.

Isoelectric focusing in layers of granulated gels. II. Preparative isoelectric focusing

A method for preparative isoelectric focusing of 0.1-10 g amounts of proteins is described. For anticonvective stabilization of the pH gradient, layers of granulated gels (E.G. Sephadex or Bio-Gel) of variable length, width and thickness were used either on glass plates or in troughs. Load capacity, defined as the amount of protein per ml gel suspension, was determined to be 5-10 mg per ml for total protein, irrespective of the pH range of the carrier ampholytes. For single proteins load capacities of 0.25-1 mg per ml were found for pH 3-10 carrier ampholytes, and 2-4 mg per ml for narrow pH range ampholytes. Experiments on a quartz plate followed by densitometric evaluation in situ at 280 nm have demonstrated that it is possible to proceed from analytical thin-layer isoelectric focusing to preparative separations without loss of resolution, just by changing the dimension of the gel layer and increasing the protein load. Improved resolution which facilitates isolation of isoelectrically homegenious components could be achieved on a 40 cm long separation distance. The geometry of a layer is favourable to heat dissipation and this permits the use of high voltage gradients. Recovery of the focused proteins is high an elution simple. The efficiency of the method is illustrated by examples showing separations of single proteins and protein mixtures.