Polyphenol oxidase properties, anti-urease, and anti-acetylcholinesterase activity of Diospyros lotus L. (Plum Persimmon)

Purification of damson plum polyphenol oxidase by affinity chromatography and investigation of metal effects on enzyme activity

Polyphenol oxidase (PPO) was firstly purified from damson plum as a high antioxidant source. PPO was treated by 0-80% ammonium sulfate precipitation and dialysis. Characterization results were determined for catechol, 4-methyl catechol, pyrogallol and caffeic acid as 0.05 M/pH: 7.2/25 °C; 0.2 M/pH: 4.5/10 °C; 0.01 M/pH: 6.8/5 °C, and 0.2 M/pH: 8.5/10 °C, respectively. V_max and K_M values were calculated for same substrates as 17,219.97 U/(mL*min) and 11.67 mM; 7309.72 U/(mL*min) and 5 mM; 12,580.12 U/(mL*min) and 3.74 mM; 12,100.41 U/(mL*min) and 6.25 mM, respectively. Catechol gave the highest V_max value among substrates. Affinity purification was performed by using Sepharose 4B-L-Tyrosine-p-aminobenzoic acid and Sepharose 6B-L-Tyrosine-p-aminobenzoic acid. Single bands were approximately observed at 50 kDa for each affinity sample in SDS-PAGE and Native-PAGE. 93.88 and 10.46 purification-folds were obtained for PPO by reference Sepharose-4B and original Sepharose-6B gels. Metal effects upon PPO activity were also investigated due to the importance of enzymatic browning in foods. Cu⁺² activation and Fe⁺² inhibition were observed with a final metal concentration of 1 mM at 219.66 and 43.18%, respectively. PPO purification from damson plum by affinity chromatography, its characterization, stability evaluation by statistically, and effects of metal ions on damson plum PPO have not been investigated in the literature.

Oxidative polymerization process of hydroxytyrosol catalysed by polyphenol oxidases or peroxidase: Characterization, kinetics and thermodynamics

Hydroxytyrosol oligomer prepared by bioenzyme shows stronger health-promoting properties than its monomer. However, the polymerization process carried out by laccase, tyrosinase or horseradish peroxidase is still lacking in term of product characterization, kinetics and thermodynamics. To achieve these aspects, ATR-FT-IR, NMR, the Michaelis-Menten equation and isothermal titration calorimetry were explored. The results showed that the identified polymers presented a CC bond and a degree of polymerization less than six. Laccase showed the greatest affinity to hydroxytyrosol via comparison of K_m and V_m. All of these polymerization processes were spontaneous and exothermic behaviuors ranging from 30 to 50 °C, and were driven by hydrogen bonds, van der Waals interactions and hydrophobic interactions. Furthermore, circular dichroism spectroscopy was used to reveal the enzymatic structural changes during the catalysis, which showed that β-sheet levels for laccase, α-helix levels for tyrosinase, and the α-helix and random coil levels for horseradish peroxidase were dramatically decreased.