Protease inhibitor (biology)

In biology and biochemistry, protease inhibitors are molecules that inhibit the function of peptidases (old name: protease, hence the term protease inhibitor). Many naturally-occurring protease inhibitors are proteins.

In medicine, protease inhibitor is often used interchangeably with alpha 1-antitrypsin (A1AT, which is abbreviated Pi for this reason). A1AT is indeed the protease inhibitor most often involved in disease, namely in alpha 1-antitrypsin deficiency.

Classification
Protease inhibitors may be classified either by the type of protease the inhibit, or by their mechanism of action.

By protease
Classes of proteases are:
 * Cysteine protease inhibitors
 * Serine protease inhibitors (serpins)
 * Trypsin inhibitors
 * Threonine protease inhibitors
 * Aspartic protease inhibitors
 * Metalloprotease inhibitors

By mechanism
Classes of inhibitor mechanisms of action are:
 * Suicide inhibitor
 * Transition state inhibitor
 * Protein protease inhibitor (See serpins)
 * Chelating agents