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 P_i for this reason)^*. A1AT is indeed the protease inhibitor most often involved in disease, namely in alpha 1-antitrypsin deficiency.

Classes of protease inhibitors are:

• Cysteine protease inhibitors
• Serine protease inhibitors (serpins)
  • Trypsin inhibitors
• Threonine protease inhibitors
• Aspartic protease inhibitors
• Metallo protease inhibitors

Biochemistry