Characterization and inhibition of Rosmarinus officinalis L. polyphenoloxidase

摘要

Polyphenoloxidase (PPO) from Rosmarinus officinalis L. was fractionated by ammonium sulfate ((NH4)2SO4) precipitation and dialysis, and then some of its kinetic properties such as optimum pH and temperature, substrate specificity, thermal inactivation, and inhibition were investigated using 4-methylcatechol, catechol, and pyrogallol as substrates. The protein content of Rosmarinus officinalis L. extracts was determined according to Bradford’s method. Kinetic parameters, K m and V max, were calculated from Lineweaver–Burk plots. According to V max/K m ratio, 4-methylcatechol was the most suitable substrate. The optimum temperature and pH values were 20, 30 and 30 °C, and 7, 8 and 8 for 4-methylcatechol, catechol, and pyrogallol substrates, respectively. The thermal inactivation of PPO was investigated at 35, 55, and 75 °C. The enzyme activity decreased with increasing temperature. The effect of different inhibitors on partly purified Rosmarinus officinalis L. PPO was spectrophotometrically investigated. For this purpose, ascorbic acid and l-cysteine were used to inhibit the activity of Rosmarinus officinalis L. PPO at different concentrations. From the experimental results, it was found that l-cysteine is a more effective inhibitor than ascorbic acid due to lower K i values.