The in vivo functioning of proteins depends critically on the chemical structure of individual peptide chains, but also on the detailed folding of the chains themselves and on their assembly into larger supramolecular structures. The molecules and their fu- tional assemblies possess a limited in vitro stability. Special methods are required for their intact isolation from the source material and for their analysis, both qualitatively and quantitatively. Proteins are also increasingly used as ¿industrial components,¿ e.g., in biosensors and immobilized enzymes, because of their specificity, selectivity, and sensitivity. This requires novel and refined proce- ing methods by which the protein isolate can be converted into a form in which it can be utilized.