Purification and characterization of two isoforms of chlorogenic acid oxidase from sweet potato cells in suspension culture

Two isoforms (PPO-E and PPO-A) of chlorogenic acid oxidase (CAO) were purif ied from sweet potato (Ipomoea batatas) cells in suspension culture and cha racterized. The isoforms were separated by chromatography on DEAE-Toyopearl and Butyl-Toyopearl. The molecular masses of PPO-E and PPO-A were estimate d to be 40 Ku and 39 Ku, respectively, by SDS-polyacrylamide gel electropho resis. The isoforms had a different optimal pH and a different Km for chlor ogenic acid from one another. In addition, 60-Ku polypeptides, which had po lyphenol oxidase (PPO) activity reacted with antibodies against PPO-E and a gainst PPO-A in immunoblotting analysis. The amino-terminal amino acid sequ ences of PPO-E and PPO-A were rather similar and resembled those of 60-Ku P POs isolated from other plants. These results suggest that PPO-E and PPO-A were isoforms of PPO in the cultured cells of sweet potato and that they mi ght be generated by carboxy-terminal processing of 60-Ku forms of PPO in vi vo.