乙烯对脂肪酶活力的直接作用及其机理初探

Direct Effect of Ethylene on Lipase Activity and Its Mechanism

研究了乙烯对脂肪酶活力的直接作用及其机理.结果表明:低浓度乙烯能使脂肪酶催化三油酸甘油酯的水解活力提高;当乙烯浓度为0.9834mmol·L-1时,酶活力提高13.0%.高浓度乙烯降低脂肪酶活力;当乙烯浓度为7.9669mmol·L-1时,酶活力下降24.5%.加入乙烯的酶最适温度向高温偏移10～15℃,而酶的最适pH值不变.在pH=7.9时,乙烯使酶活力升高较大,pH为4.5～7.5,8.5,9.5～11时酶的活力降低.加入乙烯的酶与对照相比,其紫外吸收和荧光发射强度均有较大幅度增加,荧光偏振度、比旋光度和粘度显著下降.DSC分析表明:在低温范围内酶的可逆吸热峰值温度明显高于对照,而热焓变低于对照;在高温范围内酶的不可逆吸热峰值温度和热焓变都低于对照.这些结果证实了乙烯可以直接影响酶的微环境和构象.乙烯对脂肪酶的直接作用机制可能是通过改变酶的微环境以及渗入到酶分子内部改变酶构象而引起酶活力的改变.

The direct effect of ethylene on lipase activity and its mechanism have been studied. The results showed that the lipase activity increased in the presence of ethylene of lower concentrations and the highest increased percent was 13.0% when the ethylene concentration was 0.9834 mmol·L^-1. The lipase activity decreased in the presence of ethylene of higher concentrations and the highest decreased percent was 24.50% when the ethylene concentration was 7.9669 mmol·L^-1. The optimum temperature of the lipase in the presence of ethylene increased by 10～15 ℃ compared to that in the absence of ethylene. The optimum pH of the lipase was 7.5 in the presence or absence of ethylene. In the presence of ethylene, the lipase activity increased greatly at pH 7.9, but reduced at pH 4.5～7.5, 8.5 and 9.5～11. To compare with contrast, UV absorption and fluorescence emission intensities of the lipase in the presence of ethylene were enhanced markedly, and its fluorescence polarization, specific rotatory power at 30 ℃ and the viscosity at 14 ℃ in the presence of ethylene declined obviously. Differential scanning calorimetry was adopted for studying conformational transition of the lipase in the presence or absence of ethylene. The results revealed that the peak temperature of reversible endotherm of the lipase in the presence of ethylene was higher than that of the contrast and the enthalpy was lower than that of the contrast at a lower temperature, and the peak temperature of nonreversible endotherm and the enthalpy in the presence of ethylene were lower than that of the contrast at a higher temperature. These results prove that ethylene can influence directly the microcosmic environment and conformation of the lipase. The mechanism of effect of ethylene on the lipase is probably that ethylene changes the microcosmic environment of the lipase and is embedded in the lipase inside to drive the conformational transition of the lipase.