Trypsin

Trypsin is a serine protease: an enzyme that performs proteolysis by catalysing peptide bond hydrolysis. It preferentially cuts on the C-terminus side of lysine and arginine amino acid residues, leaving the selected amino acid residue in the preceding fragment.^[ref]

The bond being broken is the backbone amide linkage, rather than the lysine or arginine amino acid side chain. A formal connectivity equation for hydrolysis isHere $R^1$ and $R^2$ stand for the connected portions of the original peptide. Actual terminal protonation and electric charge depend on pH; the equation displays connectivity. Water supplies the elements needed to form the two new ends, while the enzyme is regenerated.

Selective cutting turns an unwieldy protein into shorter peptides, making peptide mapping useful for comparing proteins. In cell culture, trypsin also helps detach adherent biological cells: the HeLa culture viability experiment provides a concrete example of its use and subsequent stopping of proteolysis. The same enzyme can therefore serve both chemical analysis and preparation of a biological cell suspension.