Posttranslational processing of the Kunitz-type potato proteinase inhibitor

The twenty-two kD Kunitz-type potato (Solanum tuberosum L.) proteinase inhi bitors (PPI) are synthesized as a preprotein with a hydrophobic signal sequ ence of forty-amino acids. A ten-amino acid peptide from the amino-terminus of the nascent 22-kD PPI was synthesized and used to produce an antibody a gainst this signal peptide for identifying the 27-kD preprotein form. Immun oblot analysis was carried out using either signal peptide antibody or anti body made to the mature form of the 22-kD PPI. The preprotein, 27-kD form w as most abundant in wounded leaves (local response) and in nonwounded leave s of wounded plants (systemic response). Using antibody made against the ma ture form of the 22-kD PPI, 22-, 23-, and 24-kD, protein forms were detecte d in tuber protein, whereas, two higher molecular weight forms (approximate ly, 27- and 28-kD) were detected in protein From leaves induced by wounding both locally and systemically. The intracellular location of the 27-kD pre protein form was also determined. The predominant forms of the 22-kD PPI fa mily appear to undergo differential posttranslational processing depending on whether they accumulate in tubers or leaves.