Assessment of polystyrene nano plastics effect on human salivary α-amylase structural alteration: Insights from an in vitro and in silico study

The study found that the enzyme activity of human salivary alpha-amylase (alpha-AHS) was competitively inhibited by nanoplastic polystyrene (PS-NPs), with a half-inhibitory concentration (IC50) of 92 mu g/mL, while the maximum reaction rate (V-max) remained unchanged at 909 mu g/mL center dot min. An increase in the concentration of PS-NPs led to a quenching of alpha-AHS fluorescence with a slight red shift, indicating a static mechanism. The binding constant (K-a) and quenching constant (K-q) were calculated to be 2.92 x 10(11) M-1 and 1.078 x 10(19) M-1 center dot S-1 respectively, with a hill coefficient (n) close to one and an apparent binding equilibrium constant (K-A) of 1.54 x 10(11) M-1. Molecular docking results suggested that the interaction between alpha-AHS and PS-NPs involved pi-anion interactions between the active site Asp197, Asp300 residues, and van der Waals force interactions affecting the Tyr, Trp, and other residues. Fourier transform infrared (FT-IR) and circular dichroism (CD) analyses revealed conformational changes in alpha-AHS, including a loss of secondary structure alpha-helix and beta-sheet. The study concludes that the interaction between alpha-AHS and PS-NPs leads to structural and functional changes in alpha-AHS, potentially impacting human health. This research provides a foundation for further toxicological analysis of MPs/NPs in the human digestive system.