Conversion of the polygalacturonase isoenzymes from ripening tomato fruits

Abstract

From pericarp tissue of ripening tomato (Lycopersicom esculentum Mill. cv. Sonato), two isoenzymes of polygalacturonase, PGl and PG2, can be extracted. With water hardly any polygalaeturonase activity is extracted; with 0.5 M NaCl predominantly PG2 is found and subsequent extraction with 1.25 M NaCI delivers mainly PGl. A partly purified PGl solution gradually decomposes into PG2. Conversion of PG2 into an isoenzyme that resembles PGl, but differs from it, can be brought about by a faetor (eonvertor) that occurs at low levels in free form in unripe and early‐ripe fruits as well as in leaves. Convertor (CV) ean be set free from PGl by a short treatment at 100°C, at which temperature the convertor activity itself also decreases.The in vitro activities and several characteristics of the isoenzymes and CV as found by us differ from that found by others, probably because of carefully optimized methods. It is suggested that the CV anchors PG2 onto the cell wall, forming PGl. Thus PGl would constitute the form that depolymerizes the peetins in the middle lamellae.