Purification and characterization of the 22-kilodalton potato proteinase inhibitors

Abstract

Three abundant proteins of approximate molecular weights of 22, 23, and 24 kilodalton (kD) were purified from potato (Solarium tuberosum L.) tubers by DEAE cellulose and CM-52 cellulose ion exchange column chromatography, electroelution, and high-pressure liquid chromatography (HPLC). Antibodies specific to the gel-purified 22-kD protein were prepared. Immunoblot analysis showed that the 22-, 23-, and 24-kD proteins were immunologically related and that these proteins were present in tubers and as higher molecular weight forms in leaves, but were not detectable in stems, roots, and stolons. The ratios of amino acid composition were compared among the three purified proteins, and the amino-terminal amino acid sequences were determined for these three proteins. All three proteins have identical amino-terminal sequences that match the deduced amino acid sequence of an abundant tuber protein cDNA.