Polymer Separation by Size Exclusion Chromatography

Proteins are the essence of life processes. DNA contains the coded information for life, and is analogous to computer software, but it is the proteins that are analogous to the hardware, that actually carry out the job. Proteins have many roles, from catalysts (enzymes), through proteins that bind and interact with other molecules to control their behaviour, to structural and storage proteins which, although less functional, are nevertheless just as essential. Some proteins are ‘solid’, e.g. the proteins in our skin; others are soluble, such as those in our blood. As with most separation procedures, those designed for proteins are designed to deal with a complex mixture of similar components, and separation often depends on slight and subtle differences between these components. Moreover, whereas some proteinsmay comprise a substantial proportion of the starting mixture, others may make up only a tiny fraction. The situation is very much like mining for minerals: Rrst, select a source that is particularly enriched in the component you want, then work on removing all those you do not want. However, protein puriRers have one advantage over miners: nobody has succeeded in Rnding the philosopher’s stone to turn base metals into gold, but molecular biologists do have the equivalent } the ability to greatly enrich the starting material with the desired protein. Consequently when talking about protein puriRcation today, it is necessary to include a discussion of techniques for production of the protein by recombinant procedures. We also refer to the overall separation processes as ‘puriRcation’, since the object is usually to obtain a homogeneous preparation of one single protein type, a ‘pure’ protein (even if this aim is not always quite achieved). Separation procedures depend on differences in properties between the components, and fortunately proteins do come in a wide range of shapes and sizes. The properties that are exploited are solubility, ionic charge, size and shape, surface features and natural biological interactions. With recombinant techniques it is possible to modify the protein’s structure so as to greatly simplify its puriRcation.