Novel hemoglobin-derived xanthine oxidase inhibitory peptides: Enzymatic preparation and inhibition mechanisms

Xanthine oxidase (XO) activity is critical to modulate uric acid and hyperuricemia. Hemoglobin was hydrolyzed by bromelain and the protease from Geobacillus stearothermophilus (GsProS8) to express excellent protein recovery rate (54.87%) and XO inhibitory activity (IC50 of 0.744 mg/mL), resulting from higher contents of tryptophan, glutamic acid and glycine. The hydrolysate was fractionated and identified three novel XO inhibitory peptides IVYPW, YPWTQ, and LITGLW (IC50 of 0.63–1.09 mM). Unlike allopurinol, IVYPW and YPWTQ were mixed-type inhibitors, whereas LITGLW was a non-competitive inhibitor. In addition to the well-recognized contribution of tryptophan, molecular docking studies revealed tyrosine residue in IVYPW and YPWTQ importantly enhanced XO inhibitory activities via hydrogen-bond and Pi-Sigma interactions with Thr1010 and His875, respectively. The total number of Pi-related interactions positively determined XO inhibition as comparing IVYPW, YPWTQ and LITGLW. This study provided a promising strategy to prepare anti-hyperuricemic peptides and understand inhibition mechanisms for the management of hyperuricemia.