BIOCHEMICAL AND IMMUNOCHEMICAL CHARACTERISTICS OF POLYPHENOL OXIDASES FROM DIFFERENT FRUITS OF PRUNUS

Polyphenol oxidases (PPOs) from five Prunus species fruits (peach, apricot, almond, plum, and cherry) have been partially purified by temperature-induced phase-partitioning in Triton X-114. The effect of pH on PPO activity with or without SDS shows that optimum pH ranges from 4 to 5.5 and that this enzyme does not occur in a latent form. Multiple forms of PPO (active and inactive) have been detected by SDS-PAGE stained with DL-Dopa and by Western blot revealed with PPO antibodies from apple pulp and broad bean leaves. We demonstrated in vitro that the multiple active forms occurred as a result of proteolysis of one major form. SDS-proteinase K digestion leads to a further resistant form in the five species studied. Under totally denaturing conditions, the main active and the proteolyzed resistant forms are, respectively, monomers of 63 and 43 kDa.