Protease inhibitor (biology)

In biology and biochemistry, protease inhibitors, or antiproteases,^[1] are molecules that inhibit the function of proteases (enzymes that aid the breakdown of proteins). Many naturally occurring protease inhibitors are proteins.^[2]

In medicine, protease inhibitor is often used interchangeably with alpha 1-antitrypsin (A1AT, which is abbreviated PI for this reason).^[3] A1AT is indeed the protease inhibitor most often involved in disease, namely in alpha-1 antitrypsin deficiency.