Enzymatic methods for cleaving proteins

There could be various reasons the protein chemist may want to break a protein of interest into fragments, but foremost among them must be the purposes of peptide mapping, primary structure determination, and preparation of particular fragments for studies relating structure and function. Proteinases (or more specifically endo-proteinases) are commonly used to generate peptides for these purposes, but the number of particularly useful and commercially available proteinases is not great. This is because enzyme specificity is an important consideration-the laboratory worker generally requires good yields of clean, pure peptides, but significantly less than 100% cleavage at some or all sites of action gives rise to a complex mixture of a large number of polypeptides.