Relative abundance and inhibitory distribution of protease inhibitors in potato juice from cv. Elkana

Protease inhibitors from potato juice of cv. Elkana were purified and quant ified. The protease inhibitors represent ca. 50% of the total soluble prote ins in potato juice. The protease inhibitors were classified into seven dif ferent families: potato inhibitor I (PI-1), potato inhibitor II (PI-2), pot ato cysteine protease inhibitor (PCPI), potato aspartate protease inhibitor (PAPI), potato Kunitz-type protease inhibitor (PKPI), potato carboxypeptid ase inhibitor (PCI), and "other serine protease inhibitors". The most abund ant families were the PI-2 and PCPI families, representing 22 and 12% of al l proteins in potato juice, respectively. Potato protease inhibitors show a broad spectrum of enzyme inhibition. All the families (except PCI) inhibit ed trypsin and/or chymotrypsin. PI-2 isoforms exhibit 82 and 50% of the tot al trypsin and chymotrypsin inhibiting activity, respectively. A strong var iation within the latter activities was shown within one family and between protease inhibitor families.