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Purification and Characterization of a Polygalacturonase-Inhibiting Protein from Apple Fruit. Chenglin Yao, Horticultural Crops Quality Laboratory, USDA-ARS, BARC-West, Beltsville, MD 20705; William S. Conway(2), and Carl E. Sams(3). (2)Horticultural Crops Quality Laboratory, USDA-ARS, BARC-West, Beltsville, MD 20705; (3)Department of Plant and Soil Science, University of Tennessee, Knoxville 37901. Phytopathology 85:1373-1377. Accepted for publication 15 August 1995. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1995. DOI: 10.1094/Phyto-85-1373.

A polygalacturonase-inhibiting protein (PGIP) was purified from mature 'Golden Delicious' apple fruit. The protein was cell wall bound and had a molecular mass of 44 to 54 kDa as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Chemical deglycosylation of purified apple PGIP released a 34-kDa polypeptide, suggesting that differential glycosylation accounted for the heterogeneity in molecular mass. Apple PGIP showed differential inhibitory activity against five polygalacturonase isozymes purified from Botrytis cinerea grown in liquid culture. However, inhibition was not detected against polygalacturonase extracted from apple fruit inoculated with the same fungus. Kinetic studies suggested a mixed-type inhibition. N-terminal amino acid sequence of apple PGIP shared 96%, 68%, and 60% identity with those from pear, tomato, and bean, respectively.