Abstract

A polygalacturonase-inhibiting protein (PGIP) was purified from immature raspberry cv. Autumn Bliss fruits using ion exchange chromatography. The protein was composed of a single polypeptide chain with M_r of 38.5 kDa and a pI residing above pH 10. Kinetic studies suggested that the inhibition was of a non-competitive nature. The PGIP inhibited 2 endopolygalacturonases (endo-PG) purified from B. cinerea and an endo-PG produced by Aspergillus niger to varying degrees but did not inhibit 2 exo-PGs purified from B. cinerea, bacterial endopectate lyases and bacterial endo-PGs. The concn of PGIP at various stages of flower and fruit development was determined. The inhibitor was not detected in the flower, but reached a max. of 69 units/g in the immature green fruit decreasing to 9 units/g as fruits matured. The N-terminal amino-acid sequence was determined.