Relationship of endopolygalacturonase activity to fruit softening in a freestone peach

Abstract

Abstract A polygalacturonase protein was purified from ripe freestone peaches ( Prunus persica L. Batsch cv. Flavorcrest). The purified polypeptide was of Mr 44000, as assessed by denaturing gel electrophoresis, was bound by the lectin Concanavalin A, and was displaced from a chromatofocussing column at pH 5.5–5.6. The enzyme was shown to be endo-acting by relating changes in substrate viscosity to the release of reducing end-groups and is described as an endopolygalacturonase [poly(1,4-α-galacturonide) glycanohydrolase EC 3.2.1.15] (endoPG). EndoPG activity in individual fruit through ripening was assessed after separating endoPG from exopolygalacturonase by column chromatography. EndoPG activity was not apparent in very firm, mature fruit. As fruit began to soften (7–10 kgf) endoPG activity was in the range 0.3 to 0.9 nmol/min/g. In softer fruit (2–7 kgf), activity was in the range 0.3 to 4.1 nmol/min/g, but it increased sharply to 7.1 to 9.3 nmol/min/g in very soft fruit with the “melting soft” character. The pattern of accumulation of endoPG activity in peach differed from that observed in tomato. However, in both of these fruits evidence is accumulating that endoPG and textural changes are not closely linked.