Partial characterization of lettuce (Lactuca sativa L.) polyphenol oxidase |
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Authors: | Serap Doğan Ümran Salman |
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Affiliation: | (1) Department of Biology, Faculty of Science and Literature, Balikesir University, 10145 Balikesir, Turkey |
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Abstract: | Polyphenol oxidase (PPO) from garden lettuce (Lactuca sativa L.) was partially purified by ammonium sulphate ((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. The total phenolic and protein contents of Lactuca sativa L. extracts were determined according to the Folin-Ciocalteu and Bradford methods, and found to be 304 mg/100 g on a fresh weight basis and 494 μg/mL, respectively. PPO activity was determined using 4-methylcatechol, catechol and
pyrogallol as substrates. Kinetic parameters, K
m and V
max, were calculated from Lineweaver–Burk plots. According to V
max/K
m ratio, pyrogallol was the most suitable substrate, followed by catechol and 4-methylcatechol. The optimum temperature and
pH values were 30, 40 and 30 °C; and 6.5, 8.0 and 7.5 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 partially purified Lactuca sativa L. PPO was spectrophotometrically investigated. For this purpose, tropolone, glutathione, ascorbic acid and 4-aminobenzoic
acid were used to inhibit the activity of Lactuca sativa L. PPO at different concentrations. From the experimental results, it was found that glutathione was found to be the most
potent inhibitor for Lactuca sativa L. PPO. |
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Keywords: | Lactuca sativa L Lettuce Polyphenol oxidase Substrate specificity Optimum pH and temperature Inactivation Inhibition |
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