The procedure is suitable for uniform gels as well as for gradient gels, e.g., 1.5 mm thick, 5 - 20% gels.

The gel slab is equilibrated in 25% (v/v) ethanol, 3% (v/v) glycerol for one hour (prolonged incubation may be needed in special cases, and the concentration of glycerol may be increased). One of the frames is placed on a clean table. The two cellophane sheets are soaked in water and one is spread out to cover the frame (Fig. 1a). About 10 ml of the equilibrating solution is poured onto the membrane in the frame. The gel is placed on the cellophane membrane in the center of the frame (Fig. 1a). The second wet membrane is then carefully placed (Fig. 1b) so that it covers the first membrane and the gel. Care is taken so that no air-bubbles are trapped between the sheets and the gel.

The second cellophane sheet may be rolled on by means of a glass rod. Or simply, holding it vertically and slowly lower it while allowing it to cover the gel from one side to the other.

The second frame is placed upon the first (Fig. 1c) resulting in the gel being sandwiched between the two cellophane sheets, which again are sandwiched between the frames. The frames are pressed together with binder clips (Fig. 1d, e). The surplus of solution between the sheets is drained off with only a few of the clips in position while forcing the frames slightly apart (Fig. 1d). the remainder of the clips (six in all for large frames, four for small frames) are then fixed.

Supported at the two short ends, the assembled frames are placed 10-15 cm above the table (Fig. 1e) and fan is placed 1-1.5 m away to supply a uniform stream of air on both sides of the horizontally placed frame (Fig. 1e). The draught in a ventilated hood is also adequate. The gel will be completely dry within 12-16 h, and may then be cut out (Fig. 1f). The gel may get wet and possibly crack if the frames are taken apart before cutting out the gel.

Densitometric scanning of the same protein pattern stained with Coomassie Brilliant Blue before and after drying is shown in Figs. 2A and B, respectively. The small differences in peak height and shape are within the discrepancies between two equally performed electrophoreses. However, there is a slight shrinking of the dried gel towards the end of the gradient (Fig. 2).

Fig. 2.
Densitometric scanning of a polyacrylamide gel electrophoresis slab before (A) and after (B) drying. The sample applied was human serum depleted of albumin by chromatography on Blue-Sepharose CL-6B (Pharmacia) [2]. The electrophoresis was performed on a vertical gel slab electrophoresis apparatus. Slab size 1 11.5 X 16.5 cm. Separator gel: 7-20% acrylamide/0.375 M Tris buffer, pH 8.9/0.1% SDS. Spacer gel: 4.5% polyacrylamide/0.125 M Tris, pH 6.7/0.1% SDS. Reservoir buffer 0.25 M Tris/0.19 M glycine, pH 8.3/0.1% SDS. The samples (100 µl with 50 µg protein) were prepared in 1% SDS, 0.01 M dithiothreitol/0.03 M Tris, pH 6.77 and heated in a boiling waterbath for 5 min. Free SH groups were, then blocked by adding iodoacetarni-de to a final concentration of 0.03 M. Electrophoresis was at 50 V for 18h at 10cg. The gel was stained in 0.1% Coomassie blue/50% methanol/10%CH3COOH, and destained in 50% methanol/7% CH3COOH, followed by 7% CH3COOH in water.

Proteins labelled with ³H, ¹⁴C or ³⁵S are detected by fluorography. Gels prepared for fluoro-graphy by soaking in DMSO with scintillator are dried directly (i.e., no equilibration with ethanol/glycerol) without any problems by the described method. The two sides of the dried gel are identical, allowing for simultaneous exposure to two films, one of which may be developed for inspection whilst the exposure of the other can be continued, provided the gel is kept in position on the film by tape.

Rehydration

Various applications may require rehydration of the gel. This may be effected by placing the gel in ethanol followed by gradual dilution with an equal volume of water. The dilution may conveniently be done by infusing the water over a 16-18 h period by means of a peristaltic pump whilst maintaining gentle mixing

Reference: Wallevik K, Jensenius JC. A simple and reliable method for the drying of polyacrylamide slab gels. J Biochem Biophys Methods. 1982 Apr;6(1):17-21.