Abstract: Eighteen aqueous extracts of medicinal plants containing crude drug 0.5 mg·μL^-1 were prepared and their inhibition rates to 5-lipoxygenase (5-LOX) activity were measured. The results showed that inhibition rate of these extracts ranged from 1.13% to 96.06%. In the test of Rosmarinus officinalis extract, the RSD (relative standard deviation) of this method was 1.17% (<2.0%) out of 4 independent parallel tests. In the test of Magnolia officinali extract, by multiple dilution it showed that there was a good linear relationship between the lg value of extract concentration and the inhibition rate in certain concentration range, with the determination coefficient of 0.958 7. The IC₅₀ of inhibitory activity of Magnolia officinalis extract was 22.38 μg·μL^-1. These results showed that inhibitory activity of various aqueous extracts to 5-LOX activity were different. This test method was demonstrated to have many merits such as easy and fast in operation, direct and stable in result, low cost, and able to quantify the accurate inhibition concentration of samples on the activity of 5-LOX.

Key words: lipoxygenase, traditional Chinese medicine aqueous extracts, inhibitory activity