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.

Key words: ethylene, lipase activity, olein, direct effect, mechanism