Effects of tea polyphenols on the activities of soybean trypsin inhibitors and trypsin

Tea polyphenols (TPs) and other materials were extracted from Chinese green tea, and their effects on trypsin inhibitors and trypsin were analysed. TPs were found to have a deactivation effect on both Kunitz trypsin inhibitor (KTI) and Bowman-Birk trypsin inhibitor (BBTI). KTI was more easily deactivated than BBTI by complexing with TPs. The deactivation effect of TPs on KTI and BBTI reached a maximum at a TP/KTI ratio of 25 and a TP/BBTI ratio of 16. However, the deactivation effect of TPs on KTI and BBTI was reduced dramatically when KTI and BBTI were already complexed with trypsin. TPs were also found to inhibit trypsin. The inhibitory activity of TPs, KTI and BBTI on trypsin was found to decrease in the order BBTI(greater than)TI (greater than) Ps. Complete inhibition of trypsin by TPs could not be achieved. When the TP concentration was increased to about 17 g ml^-1, the residual activity of trypsin was maintained at 400 TU mg^-1, equivalent to 32% of the initial trypsin activity. In TP inhibition the KM value for trypsin remained unchanged at 5.88 × 10^-4 mol l^-1 and Vmax decreased when benzoyl-DL-arginine-p-nitroanilide (BAPNA) was used as substrate. The pattern of trypsin inhibition by TPs is non-competitive.