A PROTEIN FROM IMMATURE RASPBERRY FRUITS WHICH INHIBITS ENDOPOLYGALACTURONASES FROM BOTRYTIS-CINEREA AND OTHER MICROORGANISMS

A polygalacturonase-inhibiting protein (PGIP) was purified from immatu re raspberry 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 w as of a non-competitive nature. The PGIP inhibited two endopolygalactu ronases (endo-PG) purified from Botrytis cinerea and an endo-PG produc ed by Aspergillus niger to varying degrees but did not inhibit two exo -PGs purified from B. cinerea, bacterial endopectate lyases and bacter ial endo-PGs. The concentration of PGIP at various stages of flower an d fruit development was determined. The inhibitor was not detected in the flower, but reached a maximum of 69 units g-1 in the immature gree n fruit decreasing to 9 units g-1 as fruits matured. The N-terminal am ino-acid sequence was determined.