The fabrication of multichannel tubing and its use in a continuous-flow isielectric focusing apparatus to give smooth laminar flow

Electrophoresis: the march of pennies, the march of dimes

The present review encompasses ca. 65 years of history of developments in electrokinetic separations, taking as a starting point the year 1937, i.e. the official launching of Tiselius' moving boundary electrophoresis (MBE). The 1950s have been particularly rich in introducing novel methodologies in zone electrophoresis (ZE), thus bringing about the decline of MBE. Among them of extraordinary importance was the development of electrophoresis on agar gels coupled to immuno-diffusion at right angles, which brought a big revolution not only in biochemistry but also in clinical chemistry. Also the by now forgotten paper electrophoresis was a landmark in separation science, in that it implemented, in its "fingerprinting" version, the first genuine two-dimensional (2D) map, coupling orthogonally a charge to a hydrophobic scale separation, while permitting for the first time the detection of spot mutations, i.e. single amino acid replacements in a polypeptide chain, that paved the way to modern genetic analysis. Equally important was the introduction of starch-block electrophoresis, that brought about the notion of sieving and the first discontinuous buffers, refined, in the 1960s, by Ornstein and Davies with their classical papers combining multiphasic buffer systems to polyacrylamide gels, that went down to history as disc-electrophoresis. The 1960s also contributed with two fundamental techniques, isoelectric focusing (IEF) and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) that permitted to discriminate proteins solely on the basis of surface charge and molecular mass, respectively. The 1970s gave other fundamental contributions, such as isotachophoresis, the first example of a fully instrumental approach to electrophoresis, both in its analytical and preparative version (Tachophor and Tachofrac), 2D maps combining IEF to SDS-PAGE at right angles and silver staining techniques, that incremented sensitivity by 3 orders of magnitude. The 1980s generated immobilized pH gradients and capillary zone electrophoresis (CZE), two big players that dominated the electrokinetic horizon for all the 1990s and still in vigorous use in present days. The review terminates with a glimpse, in the third millennium, onto microchip technology and hyphenated techniques, notably direct interfacing of various electrophoretic separation methods with mass spectrometry (MS).

Preparative isoelectric focusing in immobilized pH gradients. I. General principles and methodology

A new method for preparative protein purification is described, based on the use of Immobiline matrices. After electrofocusing, the protein zone of interest is recovered by electrophoretic transfer to a hydroxyapatite gel, from which it is eluted with 0.2 M phosphate buffer, pH 6.8, with yields for the proteins studied in the range 76-98%. For six different proteins, the focusing step gives a common upper limit of approximately 45 mg protein/ml gel as mean concentration in a focused protein zone. It is demonstrated that in practical preparative work, components with a pI difference of 0.007 pH units can be completely resolved, and that on a 5-mm-thick gel of dimensions 240 X 110 mm, samples containing as much as 400 mg of the major protein component can be applied. Focusing of large amounts of a salt-containing sample is demonstrated with the aid of human serum. A theoretical expression is given relating the concentration distribution and maximum protein concentration within a focused zone to the applied voltage, the pH slope used and the zone width. Based on this expression and the finding of an upper concentration limit for a protein we shown how to optimize the parameters in preparative work with immobilized pH gradients in relation to the separation power needed. Finally, it is shown that, in comparison with conventional preparative electrofocusing in polyacrylamide gels, immobilized pH gradients allow a ten-fold increase in load, whilst still giving a resolution comparable to that of analytical isoelectric focusing.