ALPHA-GALACTOSIDASE AND BETA-GALACTOSIDASE ACTIVITIES IN JUICE VESICLES OF STORED VALENCIA ORANGES

Several glycosidase activities were assessed in extracts of Valencia juice vesicles of citrus fruit. Of the enzymes assayed, α- and β-galactosidase were most active, but α- and β-glucosidase were also found. The galactosidases were partially purified and their activities assessed during eight weeks of storage at 10°. Total α-galactosidase activity remained constant but β-galactosidase declined after the eight-week storage period. Both galactosidases were resolved into two enzymatic forms by ion-exchange and gel filtration chromatography. Each enzymatic form of the galactosidases had different substrate specificities, pH optima, and responses to inhibitors. α-Galactosidase I, α-galactosidase II, β-galactosidase I, and β-galactosidase II had Km values of 0.47, 0.23, 0.27 and 0.77 mM, and apparent Mrs of 36 300, 39 800, 56 200 and 57 200, respectively. Only α-galactosidase II was able to release reducing groups from isolated cell wall material of juice vesicles. © 1990.