the study of generation of carcinogens in tobacco smoke and cooking at high heat. Laboratory applications Proteolysis is also used in research and diagnostic applications: Cleavage of fusion protein so that the fusion partner and protein tag used in protein expression and purification may be removed. The proteases used have high degree of specificity, such as thrombin, enterokinase, and TEV protease, so that only the targeted sequence may be cleaved. Complete inactivation of undesirable enzymatic activity or removal of unwanted proteins. For example, proteinase K, a broad-spectrum proteinase stable in urea and SDS, is often used in the preparation of nucleic acids to remove unwanted nuclease contaminants that may otherwise degrade the DNA or RNA. Partial inactivation, or changing the functionality, of specific protein. For example, treatment of DNA polymerase I with subtilisin yields the Klenow fragment, which retains its polymerase function but lacks 5'-exonuclease activity. Digestion of proteins in solution for proteome analysis by liquid chromatography-mass spectrometry (LC-MS). This may also be done by in-gel digestion of proteins after separation by gel electrophoresis for the identification by mass spectrometry. Analysis of the stability of folded domain under a wide range of conditions. Increasing success rate of crystallisation projects Production of digested protein used in growth media to culture bacteria and other organisms, e.g. tryptone in Lysogeny Broth. Protease enzymes Proteases may be classified according to the catalytic group involved in its active site. Cysteine protease Serine protease Threonine protease Aspartic protease Glutamic protease Metalloprotease Asparagine peptide lyase Venoms Certain types of venom, such as those produced by venomous snakes, can also cause proteolysis. These venoms are, in fact, complex digestive fluids that begin their work outside of the body. Proteolytic venoms cause a wide range of toxic effects, including effects that are: cytotoxic (cell-destroying) hemotoxic (blood-destroying) myotoxic (muscle-destroying) hemorrhagic (bleeding) See also The Proteolysis Map PROTOMAP a proteomic technology for identifying proteolytic substrates Proteasome In-gel digestion Ubiquitin References Further reading External links The Journal of Proteolysis is an open access journal that provides an international forum for the electronic publication of the whole spectrum of high-quality articles and reviews in all areas of proteolysis and proteolytic pathways. Proteolysis MAP from Center on Proteolytic Pathways Post-translational modification Metabolism EC 3.4