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 cyclins at different stages of the cell cycle.

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

Venoms
Certain venoms, such as those produced by poisonous snakes, can also cause proteolysis. These venoms are, in fact, highly-evolved 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)