Cysteine protease inhibitor that likely functions in defense against insects by inhibiting cysteine proteases in the midgut of herbivore insects such as C.maculatus (PubMed:33266031). Selectively inhibits cathepsin L, as well as papain, ficin and bromelain with lower efficiency (PubMed:33266031). Shows antitumor activity, inhibiting the growth of prostate cancer cell lines PC3 and DU145, and the gastric cancer cell line Hs746T (PubMed:33266031). No activity against cathepsin B or serine proteases (trypsin, human plasma kallikrein and elastase) (PubMed:33266031). Optimum pH is around 6. Stable from pH 2 to 10. Thermostable. Active from 25 to 100 degrees Celsius. Retains 80% of its maximal activity after heating for 2 hours at 100 degrees and retains around 30% of its maximal activity after heating for 4 hours at 100 degrees. Expressed in seeds (at protein level). Belongs to the 2S seed storage albumins family.