Purification and Characterization of Latent Polyphenol Oxidase from Apricot (<i>Prunus armeniaca</i> L.)

Polyphenol oxidase from apricot (<i>Prunus armeniaca</i>) (<i>Pa</i>PPO) was purified in its latent form (L-<i>Pa</i>PPO), and the molecular weight was determined to be 63 kDa by SDS-PAGE. L-<i>Pa</i>PPO was activated in the presence of substrate at low pH. The activity was enhanced by CuSO<sub>4</sub> and low concentrations (≤ 2 mM) of SDS. <i>Pa</i>PPO has its pH and temperature optimum at pH 4.5 and 45 °C for catechol as substrate. It showed diphenolase activity and highest affinity toward 4-methylcatechol (<i>K</i><sub>M</sub> = 2.0 mM) and chlorogenic acid (<i>K</i><sub>M</sub> = 2.7 mM). L-<i>Pa</i>PPO was found to be spontaneously activated during storage at 4 °C, creating a new band at 38 kDa representing the activated form (A-<i>Pa</i>PPO). The mass of A-<i>Pa</i>PPO was determined by mass spectrometry as 37 455.6 Da (Asp102 → Leu429). Both L-<i>Pa</i>PPO and A-<i>Pa</i>PPO were identified as polyphenol oxidase corresponding to the known <i>Pa</i>PPO sequence (UniProt O81103) by means of peptide mass fingerprinting.