3.9.1. Inhibition of Xanthine Oxidase Activity (XO)

The inhibition of XO with xanthine as a substrate was measured spectrophotometrically based on Sweeney et al. [65] with slight modification. The enzyme activity was determined at 30 °C by measuring the increase in absorbance at 295 nm over a 2min period using a microplate reader (Epoch 2 Microplate Spectrophotometer, BioTek Instruments). Ethanol instead of the sample was the control. Allopurinol was applied as inhibitor control.

The inhibitory activity (depending on the sample) was expressed as an EC₅₀-extract concentration providing 50% of activity based on a dose-dependent mode of action. The mode of inhibition on the enzyme was shown using a Lineweaver–Burk plot.