Electrophoresis
Electrophoresis is a technique in which melecules (enzymes, proteins, amino acids, nucleotides and nucleic acids) are separated by differences in their net charge in the presence of an externally applied electric field. This technique is routinely used in enzyme purification and isozyme separation in the laboratories, although it has found only limited application at large scale, since the technique is time consuming and is a bit expensive.

Various types of instrumental approaches have been used to separate and purify charged molecules using electrophoresis. However, the most common method for purifying enzymes, is through electrophoresis on polyacrylamide gel. Polyacrylamide is a polymer of acrylamide and methylene bisacrylamide, and when prepared as a gel it is transparent, thermostable, non-ionic and extremely regular in structure. The gel may be taken either in the form of a column or a slab, although the latter is preferred over the former.

A variation of the above polyacrylamide gel electrophoresis, is the sodium dodecyl sulfate-polycrylamide gel electrophoresis (SDS-PAGE), which is used to determine the molecular weight of proteins. In this method, the separation is caused by the seiving action of the gel. The proteins migrate through the gel depending on their shapes and mass/charge (m/z) ratio. Gel electrophoresis is also used to separate various isozymes of a given enzyme. Isozymes perform the same catalytic function but differ in their regulatory and some kinetic aspects.

Final processing of enzymes
Most of the commercially available enzyme preparations, purified as above, are concentrated and sterile filtered, after purification. This is done to reduce both, the volume and the microbial contamination of the sample. Often, before storage and transport, the sample is freeze-dried with additives such as sugar substrates and dextrans.