Purification and characterization of olive (Olea europaea L.) peroxidase – Evidence for the occurrence of a pectin binding peroxidase

Peroxidase from olive fruit (Olea europaea L., cv Douro) in a black ripening stage was purified to electrophoretic homogeneity, resulting in four cationic and four anionic fractions. The anionic fractions accounted for 92% of recovered activity and showed molecular masses of 18–20 kDa. The anionic fraction PODa4, the predominant fraction that comprised about 70% of total recovered activity, showed an isoelectric point of 4.4 and optimum pH and temperature of, respectively, 7.0 and 34.7 °C, and apparent K_m values of 41.0 and 0.53 mM, for phenol and H₂O₂, respectively. From the activity-temperature profile, the denaturation temperature and the changes in enthalpy and heat capacity for unfolding of PODa4 were estimated as being, respectively, 36.5 °C, 411.2 and −13.6 kJ mol⁻¹ K⁻¹. The activation energy for phenol oxidation by PODa4 was 99.1 kJ mol⁻¹, corresponding to a calculated temperature coefficient (Q₁₀) of 4. The arabinose (39 mol%) and galacturonic acid (38 mol%) content of the carbohydrate moiety indicated the existence of pectic material in the purified PODa4 fraction. Co-migration of the carbohydrate with the protein band in the isoelectric focusing electrophoresis, points to PODa4 fraction as being a pectin type binding peroxidase.