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

A polygalacturonase-inhibiting protein (PGIP) was purified from immature 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 was of a non-competitive nature. The PGIP inhibited two endopolygalacturonases (endo-PG) purified from Botrytis cinerea and an endo-PG produced by Aspergillus niger to varying degrees but did not inhibit two exo-PGs purified from B. cinerea, bacterial endopectate lyases and bacterial endo-PGs. The concentration of PGIP at various stages of flower and fruit development was determined. The inhibitor was not detected in the flower, but reached a maximum of 69 units g-1 in the immature green fruit decreasing to 9 units g-1 as fruits matured. The N-terminal amino-acid sequence was determined.