Investigation of the effects of pesticides on 'Jonagold' apple (Malus x domestica) polyphenol oxidase enzyme activity

Abstract

In this study, the effects of a number of commonly used pesticides on the activity of the polyphenol oxidase (PPO) enzyme from pesticide-free and pesticide-applied 'Jonagold' apples were comparatively evaluated. Substrates 4-methylcatechol, pyrocatechol, pyrogallol and L-tyrosine were used to determine the substrate specificity of the PPO enzyme obtained from apple. According to the results, on the contrary, PPO enzyme from 'Jonagold' apple did not show any activity against L-tyrosine substrate which is a monophenolic substrate, the enzyme had high affinity against 4-methylcatechol, pyrocatechol and pyrogallol which are di and tri phenolic substrates. Km values of PPO enzyme obtained from pesticide-free apples against 4-methylcatechol, pyrocatechol, and pyrogallol substrates were determined as followed 0.27 mM, 2.27 mM, and 0.37 mM, respectively. Vmax values were found as 0.133 mM/min, 0.081 mM/min, and 0.051 mM/min. Optimum pH values were found to be 4.5 for 4-methylcatechol, 7.0 for pyrocatechol, and 7.5 for pyrogallol. Optimum temperature values were determined as 40 degrees C for 4-methylcatechol, 10 degrees C for pyrocatechol, and 50 degrees C for pyrogallol. Km values for PPO enzyme activity obtained from pesticide-treated apples against 4-methylcatechol, pyrocatechol, and pyrogallol substrates were 0.98 mM, 3.94 mM, and 0.37 mM, Vmax values were 0.08 mM/min, 0.02 mM/min, and 0.034 mM/min. Optimum pH values were found to be 7.0 for 4-methylcatechol and pyrocatechol and 7.5 for pyrogallol. Optimum temperature values were determined as 50 degrees C for 4-methylcatechol, 30 degrees C for pyrocatechol, and 40 degrees C for pyrogallol. Overall, the results showed that the PPO enzyme from pesticide-free apples had higher activity than pesticide-treated apples. The effects of metals and storage stability on PPO enzyme activity were also investigated. The results reveal that pesticide use affects PPO enzyme activity. The obtained data bring to light new pesticide functional features of great interest in the medicinal, agro-chemical and environmental circles.