Enzymatic Characteristics and Thermal Inactivation Kinetics of Lipoxygenase from Fresh Jujube
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Abstract:
Using linoleic acid as a substrate, the enzymatic characteristics and thermal inactivation kinetics of lipoxygenase (LOX) from fresh jujube were studied by ultraviolet (UV) spectrophotometry. The effects of temperature, pH, metal ions, and complexing agents on LOX activity were investigated, and the kinetic parameters for the LOX enzymatic reaction and thermal inactivation were determined. The results showed that the maximum absorption wavelength of fresh jujube LOX was 265 nm, while the optimum temperature and pH were 40 ℃ and pH 7.0, respectively. LOX activity was relatively stable at pH 5.0~6.0. Kinetics of the enzymatic reaction followed the Michaelis-Menten equation for single-substrate enzyme-catalyzed reaction, and the values of Km and Vmax were 0.14 mmol/L and 0.26 U/min, respectively. Fresh jujube LOX showed good affinity to the substrate linoleic acid. In addition, the thermal inactivation of LOX could be described by a first-order kinetic model, and activation energy (Ea) was 105.20 KJ/mol. The enzyme activity was enhanced by 2 mmol/L Cu2+ and 10 mmol/L Cu2+, Mn2+, and Ca2+, but was inhibited by 2 mmol/L Mg2+, Zn2+, and Mn2+, as well as 10 mmol/L Mg2+ complexing agents (P < 0.05). The results provide useful reference data for the control of LOX activity during processing and storage of fresh jujube.
