The activity of proteases is inhibited by protease inhibitors. Thrombin is also inactivated by antithrombin, a serine protease inhibitor. Tenofovir interacts with didanosine and HIV-1 protease inhibitors. It contains inhibitors of multiple cysteine and serine protease families. It is an inhibitor of the enzyme transmembrane protease, serine 2 (TMPRSS2). Another proposed therapy is inhibition of viral protease or kinase enzymes. Important antiretroviral drugs include the class of protease inhibitors. One example of protease inhibitors is the serpin superfamily. Lopinavir is an antiretroviral of the protease inhibitor class. Diisopropyl fluorophosphate(DIFP) is an irreversible inhibitor that blocks the action of serine protease. This gene encodes a protein that belongs to the serine protease family. Active site cysteine residues are the functional unit in cysteine protease catalytic triads. The plant meanwhile secretes esterase, peroxidase, phosphatase and protease enzymes. Subtilisin is a serine protease in prokaryotes. Resistance to some protease inhibitors is high.