POLYGALACTURONASE, CELLULASE AND INVERTASE ACTIVITIES DURING CHERIMOYA FRUIT RIPENING

The activities of the cell-wall degrading enzymes polygalacturonase (P G) and cellulase and of two forms of invertase were studied during the ripening of cherimoya fruit. All activities showed maxima coinciding with the climacteric maximum in respiration and the beginning of the m ost pronounced rise in ethylene production. The activities of PG and c ellulase increased three-fold concomitantly with the highest drop in f lesh firmness. After reaching maxima, the activity of the soluble inve rtase was almost stabilized, while that of the cell-wall bound form de creased to values similar to those of preclimacteric fruit. Since fruc tose and glucose concentrations increased continuously during ripening it is suggested that sucrose was hydrolyzed mainly by the soluble inv ertase. Cherimoya PG and cellulase had maximum activities at pH 5.0 an d 5.5, respectively. PG activity was more thermostable than cellulase activity (complete inactivation by heating for 5 min at 75 degrees C a nd 60 degrees C, respectively). The activity of both invertases had a similar pH optimum (3.0-3.5), heat stability (complete inactivation by heating for 5 min at 55-60 degrees C) and affinity for sucrose (K-m o f 2.6 and 3.8 mM).