Inhibition mechanism of phloretin on grass carp myofibril-bound serine proteinase: From inhibition type to structural and interaction alterations.

This study aims to investigate the inhibitory effect of phloretin on myofibril-bound serine proteinase (MBSP) activity in grass carp and its underlying mechanism. The results showed that phloretin acted as a reversible competitive inhibitor of MBSP. Phloretin exhibited static quenching of MBSP, and it primarily interacted with MBSP through hydrogen bonds and van der Waals forces, with at least one optimal binding site on MBSP. Concurrently, molecular dynamics simulations confirmed the binding affinity was stronger at 55 °C compared to 4 °C. With rising phloretin concentration, the α-helix content of MBSP first increased and then decreased, an effect more pronounced at 55 °C. MBSP surface hydrophobicity decreased initially before increasing, while mean size and PDI value gradually increased, with both trends being more evident at 55 °C. These findings could provide guidance for the use of phloretin as a natural inhibitor of MBSP and for enhancing the quality of heat-processed aquatic products.