KUNITZ-TYPE PROTEINASE-INHIBITORS FROM INTACT AND PHYTOPHTHORA-INFECTED POTATO-TUBERS

Three protein proteolytic enzyme inhibitors with molecular masses 21, 22, and 23 kDa have been isolated from intact potato tubers (Solanum t uberosum L. cv, Istrinskii). The 21 and 22 kDa proteins denoted as PSP I-21 and PSPI-22, respectively, are serine proteinase inhibitors with different specificity. The 23 kDa protein denoted as PCPI-23 is an inh ibitor of plant cysteine proteinases, The PSPI-21 molecule consists of two disulfide-linked polypeptide chains with molecular masses of 16.5 kDa and 4.5 kDa, The PSPI-22 and PCPI-23 hale one polypeptide chain, Their amino-termini numbered 21-25 amino acid residues have significan t homology to other plant inhibitors which are members of the soybean Kunitz inhibitor family, It is found that at least PSPI-21 and PSPI-22 can predominantly accumulate in potato tubers infected with Phytophth ora infestans zoospores, (C) 1998 Federation of European Biochemical S ocieties.