to prevent substrate access. In competitive inhibition, the inhibitor binds to the active site, thus preventing enzyme-substrate interaction. In non-competitive inhibition, the inhibitor binds to an allosteric site, which alters the active site and makes it inaccessible to the substrate. Examples of protease inhibitors include: Serpins Stefins IAPs Uses Potential pharmaceuticals Currently there is no widespread use of cysteine proteases as approved and effective anthelmintics but research into the subject is a promising field of study. Plant cysteine proteases isolated from these plants have been found to have high proteolytic activities that are known to digest nematode cuticles, with very low toxicity. Successful results have been reported against nematodes such as Heligmosomoides bakeri, Trichinella spiralis, Nippostrongylus brasiliensis, Trichuris muris, and Ancylostoma ceylanicum; the tapeworm Rodentolepis microstoma, and the porcine acanthocephalan parasite Macracanthorhynchus hirundinaceus. A useful property of cysteine proteases is the resistance to acid digestion, allowing possible oral administration. They provide an alternative mechanism of action to current anthelmintics and the development of resistance is thought to be unlikely because it would require a complete change of structure of the helminth cuticle. In several traditional medicines, the fruits or latex of the papaya, pineapple and fig are widely used for treatment of intestinal worm infections both in humans and livestock. Other Cysteine proteases are used as feed additives for livestock to improve the digestibility of proteins and amino acids. See also Protease Serine protease Threonine protease Aspartic protease Metalloprotease Enzyme Proteolysis Catalytic triad Convergent evolution PA clan The Proteolysis Map Protease inhibitor (pharmacology) Protease inhibitor (biology) TopFIND – database of protease specificity, substrates, products and inhibitors MEROPS – database of protease evolutionary groups References External links The MEROPS online database for peptidases and their inhibitors: Cysteine Peptidases Proteases