PURIFICATION OF 3 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 (Prun us 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 protei ns were N-terminally blocked but amino acid sequences were obtained fo r peptides released from two of the three isoforms. The sequences reve aled a threonine/lysine substitution in a comparison between isoform P E2/isoform PE3, and there were regions of sequence similarity with oth er 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 al so bound to isoforms PE1 and PE2. The study provides the enzyme protei n sequence and immunological basis for an evaluation of the role of pe ctin esterases in normal and abnormal ripening of peach fruit.