The flexibility and usefulness of polyacrylamide gel-slab isoelectric focusing is greatly increased by performing separations with glass slides embedded in the gel. After separation, each gel-coated slide can be treated separately; as many as eight individual reactions can be observed after a single electrofocusing or electrophoresis run. Other modifications described include the simultaneous electrofocusing of two different gel compositions and a simple technique for permanent recording which does not require photography.
Isoelectric focusing, the separation of molecular species by isoelectric point, has proven to be a sensitive, reproducible technique, particularly valuable in the separation of closely related proteins which may not be easily separable by other physical techniques. The combination of the principles of isoelectric focusing with the use of the stable matrix of polyacrylamide gels has added a further advantage, and finally the use of this combined technique with the gels in the form of large, thin slabs has provided a uniform pH gradient which permits the sharp separation of protein species and the concomitant side-by-side comparison of multiple samples.
Certain difficulties and disadvantages are, however, inherent in this gelslab system. Chief among these are:
(a) Exposing the polymerized gel slab is a somewhat tricky procedure which can lead to air bubbles, if not to total separation of the gel slab from the base plate.
(b) Permanent recording of the results is not simple, and storage of whole gels, though possible, is awkward.
(c) Only one composition of gel can be tested at a time. This is not a common concern, but it is sometimes desirable, as noted below, to be able to compare two gel compositions in a single run.
(d) To determine the final position of the separated protein species, the entire slab must generally be immersed in, or at least covered with, an incubation mixture of some sort. Even if this is done in a fairly closely fitting container, rather large amounts of solution are required. If the incubation mixture is a simple protein stain, the solution volume is not an 533