Proteolysis

Proteolysis is the directed degradation (digestion) of proteins by cellular enzymes called proteases or by intramolecular digestion.

Purposes
Proteolysis is used by the cell for several purposes. They include:
 * Removal of N-terminal methionine residues after translation.
 * Removal of the signal sequence of peptides after their transport through a membrane
 * Separation of viral proteins that were translated from a polycistronic mRNA
 * Digestion of proteins from foods as a source of amino acids
 * Conversion of predecessor-proteins (proenzymes, zymogens, prehormones) into their final structures.
 * Degradation of unneeded or damaged proteins for example cyclins at different stages of the cell cycle.

Proteolysis is also used in research and diagnostic applications:
 * In-gel digestion of proteins after separation by gel electrophoresis for the identification by mass spectrometry.
 * Digestion of proteins in solution for proteome analysis by liquid chromatography-mass spectrometry (LC-MS).

Examples
Examples of serine proteases include:
 * trypsin
 * chymotrypsin
 * elastase
 * papain

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)