Purification and changes in activities of tomato pectinesterase isoenzymes

Changes in the isoenzymes of pectinesterase were studied during the development of normal tomato fruit and of fruit from two near isogenic lines containing the ‘Never ripe’ ( Nr ) and ‘ripening inhibitor’ ( rin ) alleles. Nr fruit ripen slowly to an orange‐red while rin is even more extreme, eventually turning yellow. Enzyme activity present in normal green fruit increases during ripening, as did that in Nr fruit. No comparable increase was observed in rin fruit. Pectinesterase activity was resolved into two major forms by ion‐exchange chromatography. One of these isoenzymes (PE 2) accumulated during the ripening of normal and Nr fruit, but did not change in the rin fruit. PE 2 was purified to homogeneity, judged by electrophoresis in dodecyl sulphate‐polyacrylamide gels.