2 FORMS OF EXOPOLYGALACTURONASE INCREASE AS PEACH FRUITS RIPEN

Abstract. Freestone peach cultivars are distinguished from clingstone cultivars by a more extensive softening of the mesocarp tissue, and by the separation of mesocarp and endocarp during ripening. Cultivars of both types have been reported to develop exopolygalacturonase activity during ripening, but the enzyme has not been characterized in any detail. During development of freestone peaches (Prunus persica L. var Coronet), two exopolygalacturonase enzymes were detected 42, 65 and 85 d after full bloom and in ripe fruit. During ripening one enzyme (exoPG 1) increased 36‐fold and the other (exoPG 2) 90‐fold but exoPG 2 accounted for a 73% of the total activity in ripe fruit. ExoPG 1 was purified 24‐fold and exoPG 2 540‐fold. ExoPG 2 is a slightly acidic glycoprotein. ExoPG 1 and exoPG 2 differ slightly in their pH optima and in their responses to calcium: each produces monogalacturonic acid as a reaction product. Similar enzymes were found in Flavorerest, a semi‐freestone peach. Copyright © 1990, Wiley Blackwell. All rights reserved