Abstract: Natural products with inhibition of xanthine oxidase (XO) activity were screened from sunflower calathide. XO was used as a carrier to specifically adsorb and isolate candidate compounds from sunflower calathide extracts, and they were identified by high-resolution liquid mass spectrometry (LC-MS) to study the inhibitory activity and inhibition mechanism of possible compounds on XO. Thirteen compounds were isolated from the ethanol extract of sunflower calathide, including cafestol (IC50=47.49 μg/mL,P<0.0001), which exhibited competitive and reversible inhibition against XO. Circular dichroism with molecular docking verified that cafestol could bind to XO and interact with it and reduce its activity. The binding of cafestol to the FAD region of the enzyme hindered the electron transfer during the substrate oxidation reaction, making the structure of the enzyme more dense, and the substrate was difficult to locate into the active cavity, resulting in a decrease in its catalytic activity. The quenching mechanism of cafestol against xanthine oxidase belonged to static quenching, and the main driving force was hydrophobic, and cafestol had only a single or one binding site on the XO active cavity. The results showed that cafestol was a potential ingredient that inhibited XO activity, which provided a scientific basis for the screening of therapeutic drugs such as hyperuricemia.

Key words: sunflower calathide, XO, cafestol, UF-LC-MS, uric acid