Purification of three pectin esterases from ripe peach fruit

Three isoforms of pectin esterase (PE1-PE3) (pectin pectyl-hydrolase, EC 3.1.1.11.) were purified to homogeneity from ripe peach fruit (Prunus persica cv. Coronet). The three enzymes were basic proteins of M(r) 34,000 as determined by denaturing polyacrylamide gel electrophoresis but were separated by FPLC cation-exchange chromatography. The proteins were N-terminally blocked but amino acid sequences were obtained for peptides released from two of the three isoforms. The sequences revealed a threonine/lysine substitution in a comparison between isoform PE2/isoform PE3, and there were regions of sequence similarity with other plant pectin esterases. The proteins did not bind to concanavalin A and were not stained by the periodate-Schiff reagent suggesting a low or zero level of glycosylation. Polyclonal antisera to isoform PE3 also bound to isoforms PE1 and PE2. The study provides the enzyme protein sequence and immunological basis for an evaluation of the role of pectin esterases in normal and abnormal ripening of peach fruit.